The backscattered light diagnostic technique has been developed on Shen Guang-III laser facility. After using three improvements, the backscattered light can be measured quantitatively. With the rectangle hole, the dispersion effect caused by the wedge lens can be removed. With the full aperture light and white light, the transmission of the backscattered diagnostic system can be obtained. After optimizing the diagnostic system, the spectrum and time process of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) can be achieved. From the experimental data, the backscattered light diagnostic technique on Shen Guang-III laser facility has the primary ability to investigate the effect of laser and plasma interaction (LPI) and laser smooth technique.