Temperature difference and satellite vibration lead to in-orbit space camera defocused and deteriorated image quality. The wave front coding technology can extend the depth of focus without changing the optical system structure, which makes MTF insensitive for defocus. The wave front coding technology was applied to TMC system. Optimized to the best surface type, the phase mask plate was placed in the exit pupil. The imaging characteristics of the original system and wave front coding system were analyzed and evaluated. And the phase parameter which was related to the extended ratio of depth of focus and image quality was aslo analyzed. Theory and simulation results show that the application of wave front coding technology on TMC system can be easy to extend the depth of focus. It is concluded that the wave front coding technology has high practical value to solve the imaging defocused.