Laser processing 3-D microstructures inside KDP crystals is an effective way to suppress the transverse stimulated ramam scattering（TSRS）in high power lasers. A simulation study on the transmission characteristics of focused laser inside KDP crystal was carried out to investigate the feasibility of laser processing 3-D microstructures and the effects of laser parameters on the machining accuracy, efficiency and yield. The effects of the peak power density, spot distortion and deviation of laser focus are the main factors on the machining accuracy and crystal fragmentation. The size and shape of the e-ray focus will distort and its peak power density decreases rapidly with the increasing of angle between incident laser and crystal optical axis. The results show that the effect of the e-ray will make the processing efficiency increase more than double when the angle is less than 15°, and can be neglected in the low-energy or easily causes crystal fragmentation in high-energy when the angle is greater than 30°, in this case the e-ray should be shielded. The related simulated results have an important engineering value on increasing the accuracy
of laser micromachining birefringent materials.