Abstract: By analyzing the limitations of traditional birefringent crystal depolarizer, a new kind of depolarizer was designed for monochromatic pulse light. This depolarizer is made up of two quartz crystal wedges, and the angle between the two wedgesoptical axes is 45. The results of theoretical calculation show that this device can depolarize monochromatic pulse light. Software simulation based on the advanced system analysis program (ASAP) shows that emergent lights degree of polarization (DOP) is less than 0.00126. This depolarizer can depolarize mono-chromatic light with arbitrary polarization state, and it also works for quasi-monochromatic light. Besides, the depolarization results are independent of time domain.