The invention belongs to the field of design projection equipment optical systems, particularly relates to a projection optical
system improving a light
utilization rate and projection brightness, andaims to solve the problem of low light
utilization rate and
complex system structure which exist in the prior art. Polarized light P emitted by a
laser source passes through a convergent mirror and is transmitted by a polarized
beam splitter prism, polarized light P transmitted by the polarized
beam splitter prism passes through a
color wheel, an integral
square rod and a
relay lens group in sequence and is incident to a DMD, emergent light in a
projection direction of the DMD is emergent through a project lens, emergent light in a non-
projection direction of the DMD passes through a
reflex lens group to obtain polarized light S, and polarized light S reflected by the polarized
beam splitter prism and the polarized light P transmitted by the polarized beam splitter prism are coaxially incident to the
color wheel; and the
reflex lens group includes a total reflector A, a
relay lens group B, a total reflector B and a 1 / 2 wave plate; and the emergent light in the non-projection directionof the DMD is sequentially reflected by the total reflector A and refracted by the
relay lens group B and 1 / 2 wave plate to obtain polarized light S.