The saturation of stimulated Raman scattering （SRS） through Langmuir decay instability （LDI） and electron trapping in laser-plasma interaction process is studied. Analytical expressions for the saturation time of SRS are obtained for both the LDI and electron trapping schemes in 1-D homogeneous plasma irradiated by unrelativistic laser beams. The simple analytical model agrees well with numerical simulation and experiment in respect of the dependence of the saturation time of SRS on the parameters of lasers and plasmas.