Abstract: The molecular configuration of diphenyl ether has been studied by MNDO method, The most stable configuration of diphenyl ether was obtained by means of optimization of molecular geometric configuration. The rotational potential surface describing internal rotation about the two C—O bond of diphenyl ether was drawn. The calculated results show that the minimum of the rotation potential surface is at θ=φ=65°, ∠COC=120.46° and the two benzene rings are easy to rotate about the two C—O bond within certain range. The three configurations which had been considered as the most stable configuration are discussed in this paper.