Here is a brief description of The Urantia Book from its official web site:
The Urantia Book, first published by the Urantia Foundation in 1955, was authored by celestial beings as a special revelation to our planet, Urantia.
The book's message is that all human beings are one family, the sons and daughters of one God, the Universal Father. It instructs on the genesis, history, and destiny of mankind and on our relationship with God. It also presents a unique and compelling portrayal of the life and teachings of Jesus, opening new vistas of time and eternity, and revealing new concepts of Man's ever-ascending adventure of finding the Universal Father in our friendly and carefully administered universe.
Whatever it claims to be, The Urantia Book contradicts the Bible. It calls the creation week a legend and the Flood of Noah's time a lie devised by a Jewish priest during the Babylonian captivity. It states that the tree of the knowledge of good and evil is a myth, that Adam and Eve ate from the tree of life, that Jesus Christ and Michael are one and the same, and that Jesus was not tempted in the wilderness for forty days.
These are but a few of the ways in which The Urantia Book disagrees with the Bible, which tells us, "All Scripture is given by inspiration of God" (II Timothy 3:16). God does not contradict Himself. From this we can conclude that The Urantia Book is not inspired by God. In fact, our observation is that it would tend to confuse and deceive.
Moreover, its advocates are not in the least reticent to claim it was inspired by "celestial beings," rather than by God Himself. This should cause a true Christian at least some skepticism about its origins. Satan the Devil and his demons are known for their lies and deceptions (John 8:44; Revelation 12:9). Paul says our fight is not "against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places" (Ephesians 6:12). He warns that even these evil beings can seem "good" and "glorious": "For such are false apostles, deceitful workers, transforming themselves into apostles of Christ. And no wonder! For Satan himself transforms himself into an angel of light" (II Corinthians 11:13-14).
In sum, The Urantia Book should be treated with the same spiritual disdain as the prophecies of Nostradamus and Edgar Cayce and some of the other New Age and celestial spirit-inspired revelations.