The density, temperature and length of the plasma used in the backward Raman amplification will all influence the result. To explore the influence of the plasma density and the pump intensity, this work uses the one-dimensional particle in cell (PIC) algorithm to simulate the process of the 800 nm pump laser injecting into the plasma. By analyzing the Raman scattered light, it is found that as the density of plasma increases, the wavelengths of the scattered light shorten. It is also found that the forward Raman scattering will cause the plasma density to change, which in turn influences the scattered light wavelength. Therefore, we should choose the plasma density based on the wavelength of the pump and the scattered light, while the amplification of the scattered is related to the pump intensity.