To optimize a gas-stimulated Raman scattering system, the phenomenon of gas-stimulated Raman scattering was demonstrated through a combination of theory and experiments. The Raman gain coefficients of CH4 and D2 at different pressures were calculated theoretically. Stimulated Raman scattering experiments were then conducted using a 355 nm Nd∶YAG laser with an output energy of 70 mJ. The output energies of Stokes light at gas pressures of 1×105 and 2×106 Pa and focal lengths of 500 and 750 mm were measured. It is found that the CH4 Raman gain coefficient increases with an increase in gas pressure. In addition, the D2 Raman gain coefficient reaches the maximum at approximately 1×106 Pa and then do not change with increase in gas pressure. Experimental results indicate that reasonable values for Raman cell gas pressure and focal length of the coupled focusing lens must be selected for gas-stimulated Raman device applications. For example, a longer focal length and a higher pressure must be used for a methane gas system, whereas a longer focal length and lower pressure must be used for a helium system. The theoretical calculations corresponded with the experimental results. These research results shall play a major role in optimizing the light source of NO2 differential absorption laser radar.