From the view of balancing the contrast of two imaging optical paths, a practical mini-optical engine of liquid crystal on silicon (LCoS) stereoscopic projector is designed. The engine is composed of two LCoS panels to modulate the left and right images respectively, with a white LED as light source and two standard MacNeille polarization beam splitter (PBS) to generate two linear polarized beams with orthogonal polarized state. The whole optical engine has a simple design and compact structure with the size of 105 mm×28 mm×25 mm. Actual parameters of every part in our optical engine are measured. Based on these values, the calculated contrast and the light efficiencies of the right and left eye paths are 641 and 3.61% respectively, and the total light flux is about 20 lm.