The offset angle, which is adjustable, is a key parameter of gas wave refrigerator, affecting refrigeration performance. When the high pressure moist gas injects into the oscillation tube of the refrigerator, the non-equilibrium condensation will occur. Phase transition will impact the wave system in the tube and then change the optimal offset angle of the gas wave refrigerator. In this paper, a 2D model of the non-equilibrium condensation in oscillation tube is established to investigate the condensation influence on the optimal offset angle. The results show that: at constant offset angle, with the increase of rotation speed, refrigeration efficiency raises first and then decreases resulting from wave system difference. It shows optimal offset angle truly exists under every working condition, going for optimal wave system match. Condensation process will cause temperature-jump and condensation compression wave which affects wave system in the tube, so the optimal offset angle changes. Since the final Mach number of shock wave increases linearly with the raise of RH (0~0.8), the optimal offset angle decreases linearly. When RH= 0.8, the optimal offset angle decreases by 7%.