Reducing the radiometric calibration uncertainty of the space ultraviolet remote sensing instrument (SURSI) in laboratory is very important to improve the instrument′s detection accuracy in orbit. A deep study on the calibration environment of SURSI is made. The Al+MgF2 film reflectivity of 250~400 nm in vacuum/air environment are calculated by the film electromagnetic theory and two results are compared. The experiment is completed, which is study on the discrepancy in the SURSI spectral responsivity when it is at different environments by establishing SURSI responsivity vacuum/air comparison system. The average deviation is about 3.8% from 250 to 400 nm. Theoretical analysis and measurement result show that because they are affected by the optical properties of Al+MgF2 film which are decided by optical components inside the SURSI, the spectral responsivities of SURSI have distinct difference in vacuum/air environment and the deviation depends on wavelength. It is necessary to make the radiation calibration of SURSI in vacuum environment.