In the Bible it says [Gen 3:8]: "And they heard the sound of the Lord God walking in the garden in the cool of the day". It seems God has carnal body (thus he could walk). In Judaism compared with Christianity and Islam, they often think God is not in a visible form. So my question is 'is it real that God has a body in Judaism'?
The short answer to your question is "no", and that references to God's body in the biblical and rabbinic literature need to be understood figuratively. That said, there's a lot more to this than just "no", and there have been many religious Jews throughout history who have believed that God does (or at least can) possess corporeal form.
In his commentary on Tractate Sanhedrin in the Mishna, the Rambam (12th century) delineated thirteen principles that, at the time, he held to be crucial to Judaism. His third principle states that God does not possess a physical form. People tend to cite that principle today in asserting God's incorporeality.
Prof. Marc Shapiro wrote a book entitled The Limits of Orthodox Theology: Maimonides' Thirteen Principles Reappraised (Oxford, 2005), and in chapter 3 (45-70) he goes into some detail, listing the various rabbinic authorities throughout the ages who have either supported the view that God possesses physical form or who have disputed with the Rambam over his making it necessary to believe that God does not.
For an interesting example of an ancient text that discusses God's dimensions, and that the Rambam was influential in having destroyed, see Gershom Scholem's On the Mystical Shape of the Godhead (New York: Schocken Books, 1991) - in particular, pp15-37.
The earlier answer by Shimon bM addresses God's corporeality; I'll take another tack and address your reading of Genesis 3:8. You say it implies God's corporeality by saying He was walking through the garden; in fact, though, the plain reading IMO is that God's sound, not Himself, was walking (i.e., traveling, moving) through the garden, and this is the reading clearly favored by various commentators quoted by Nachmanides in his commentary.
Rabbi Mosheh Aberbauch taught me that many people believed G-d has a body, including Jews in error.
Rambam composed his text, "Dalilath Alha'irin" Guide for the Perplexed to explain "the arm of God, hand of God, vayichar af HaShem (lashon kinuyim) figure of speech. Thus he defended the fundamental beliefs 13 Iqarim. Rambam successfully confronted many ancient Greek philosophical arguments as well as contemporary Theology of the surrounding religions perplexing the Jewish thinker, to prove Torah is still the superior stable path.
While I agree that Gen. 3:18 doesn't prove HaShem in a corporeal form, there are many manifestations of HaShem throughout the Torah and the Prophets. When someone denies that HaShem can take a shape I inquire of their opinion of Number 12:8:
With him I speak mouth to mouth; in a vision and not in riddles, and he beholds the image of the Lord. So why were you not afraid to speak against My servant Moses?
One can explain away this all one wants, but the issue is the word for image is וּתְמֻנַ֥ת, this is the same word used in Exodus 20:4 where we are told:
You shall not make for yourself an idol, or any likeness of what is in heaven above or on the earth beneath or in the water under the earth.
The word for likeness is תְּמוּנָה.
Again in Deut. 4:12:
The Lord spoke to you out of the midst of the fire; you heard the sound of the words, but saw no image, just a voice.
The word for image is תְמוּנָ֛ה the same word. So the very thing HaShem said not to make of Him, He shows up in to Moses.
I have never had anyone provide an acceptable answer to Numbers 12:8 when they agree that God takes no corporeal form.
God cannot have corporeal form because that would mean that He exists inside a framework of existence.
Hence, His existence would depend on the existence of that framework.
This is a contradiction since God is the fundamental and necessary existence which depends on nothing. The corporeality ascribed in scripture is only for our understanding as the shaar yichud of chovos halevavos says in ch.10
Likewise, we must be careful regarding His attributes, whether those which describe His glorious essence or those the prophets ascribe to Him - not to take them literally or according to what would seem in a physical sense.
Rather, we must know clearly that they are in a metaphorical and incidental sense according to what we are capable of grasping with our powers of recognition, understanding, and intellect, due to our crucial need to know Him and His loftiness. But He is infinitely greater and loftier above all of this, and like the verse says "Blessed be Your glorious Name, that is exalted above all blessing and praise" (Nehemiah 9:5).
One of the philosophers said: "He whose mind is too weak to understand the matter of divesting, he holds fast to the terms in the Divinely given scriptures, and does not realize that the terms in scripture are adapted to the intelligence of those to whom they were addressed, not according to (the intelligence) of the One who addressed them. Rather they are like the whistling call to a herd of cattle at the time of water drinking, which brings them to drink far more effectively than clear and accurate words."