Abstract: The characteristics and optical path difference of beam reflected by cubecorner prism(CCP) with dihedral angle errors were researched; the CCP with errors acts as a phase screen comprised 6 optical wedges. The positions at cavity mirror of ray which propagates back and forth in the CCP laser resonator are analyzed, it shows that the CCP resonator with three equal dihedral angle errors (three dihedral angle errors are not 0) is an unstable resonator. The CCP laser resonator mode is simulated with FoxLi numeric method. The result shows that the CCP resonator oscillates typically in TEM03 mode of LaguerreGaussian beam. The beam pattern consists of 6 pieces and looks like an asterisk. The pieces of the pattern are not symmetric and equal when the 3 dihedral angle errors are different. In