The invention discloses a 90-degree spatial optical mixer with optimized polarization parameter configuration, belonging to the field of wireless communication technology. The 90-degree spatial optical mixer aims to solve the problem of lowered mixing efficiency caused by the polarization state mismatch between a local oscillation light and a signal light in the existing 90-degree spatial opticalmixer. The mixer comprises a local oscillation laser, a first half-wave plate, a quarter-wave plate, a second half-wave plate, a first polarization beam splitting prism, and a third half-wave plate, asecond polarization beam splitting prism, a first right-angle roof prism, a first balanced detector, a non-polarization beam splitting prism, a fourth half-wave plate, a third polarization beam splitting prism, a second right-angle roof prism, a second balanced detector , a right-angle prism, a polarization state detector, and a polarization state controller. The 90-degree spatial optical mixer with optimized polarization parameter configuration of the present invention gains wide application prospects in the fields of inter-satellite, satellite-ground wireless laser communication, and the construction of an air-space-ground integrated information network.