Abstract: The backscattered light diagnostic system is an important measurement tool for the ICF experiments. The basic configuration and the optical path of the backscattered light diagnostic system implemented on Shenguang Ⅲ prototype facility are summarized in the paper. Aiming at improving veracity and simplifying the calibration process, a novel full aperture light beam calibration method of transmission and spectrum response is described in the paper. High power laser and white Xe lamp are chosen as calibration resource and a peculiar optical path is erected for modulating the light beam into a full aperture distribution so that the distributing of the backscattered light on the diagnostic system are simulated. Using the method, the transmission and spectrum response are calibrated and several data are shown in the paper. The calibration results show that the SRS branch has a limited wavelength of 400 nm while the path has a poor transmittance at 527 nm.