A projection device capable of effectively performing the light utilization is disclosed, particularly comprising polarized beam components and reflective components regarded for controlling polarizing of light, reducing light missing during light transferring from a light source to a projection lens set, increase light utilization efficiency, wherein the polarizing beam components are regarded for separating the light into two orthogonal polarization waves; the present invention further comprises two modulated diaphragms regarded for controlling the strength of said two orthogonal polarization waves, equaling brightness of the polarization waves at final vision, keeping a good quality in final vision.