Abstract: The modes of stable resonator which consist of thermal distorted flat and concave mirror are investigated with Fox-Li iteration. The amplitude and phase distrigutions on the output mirror are psented. For this stable resontor, in orderto erase the mode's distribution the thermal distortion of both mirror distortion is greater than 1/10 wavelength, there would be no fundamental mode. It is also pointed out that there are more serious mirror thermal distortion in fringe cooling mirror in high power laser and then the laser beam quality is lowered badly.