The present research seeks to explain and examine the reasons for the unity of the divine essence in two stages: one in the sense of oneness and the other in the sense of unity in Islamic philosophy. The methodology of the problem of oneness and simplicity of God is such that since simplicity is opposite to compositeness, philosophers have studied the types of composites in possibilities and have then offered several reasons for denying all these composites in the divine essence of God the Exalted and thus proved the simplicity and oneness of God. Since God is the absolute being and the simple and absolute being is not confined to any limit, God is infinite and unrepeatable and is one while being simple. The results of this research show that Muslim philosophers believe in the unity of the necessary being at the top of the system of being for which there is no reason or cause and no nature and rational form; the unity of the necessary being is not characterized by the rules of nature, and is at the same time simple and one with no parallel or partner.