The first Stokes radiation (S1, 395.6 nm) of SRS of CH4, pumped by a pulsed Nd:YAG laser at 355nm, is used as λon of NO2-DIAL. A numerical study is done, aiming to explain qualitatively the practically important physical behavior of the configurations. And a series of experiments are reported here on the generation of Stokes orders generated in CH4. By adjusting pumping laser energy, beam quality and the pressure of gas, the relationship between them and the energy conversion efficiency of scattering radiations is obtained. Finally, the appropriate condition to optimize S1 is found.