The hemisphere transmittance of transmission diffusers in space remote sensing instruments changes because of the solar vacuum ultraviolet radiation, which will affect the on orbit calibration result of instruments. The characteristics of solar ultraviolet radiation spectra and the UV irradiation dose are analyzed when diffusers are on orbit, a standard deuterium lamp is used as the light source for solar ultraviolet spectrum simulation at 115~200 nm, the fused quartz diffuser is irradiated at a specific distance. After 48 h solar ultraviolet irradiation, the fused silica diffuser′s hemisphere transmittance in 250~1000 nm decrease, the degradation at 250 nm is about 3%, in the change near-infrared wavelength is less than that in ultraviolet, and the degradation at 1000 nm is about 1%, after the diffuser is washed, the hemisphere transmittance returns to the original value.The test results show contamination that on the diffuser is a major factor for the hemisphere transmittance degradation, the result is very important for transmittance diffuser protection, on-orbit calibration and degradation correction.