The principle of wedge-crystal depolarizer was introduced and an optimal parameters combination of polarization direction, wedge angle, pupil size was obtained by using Mueller matrix. The design of depolarizer should be determined by crystal refraction index, wavelength, and incident pupil size. Calculation and simulation based on software show that degree of polarization (DOP) can be improved by increasing pupil size and wedge angle. Some significant conclusions for the optimized design of parameters were gained for fabricating crystal depolarizers.