Stimulated Raman scattering (SRS) can affect the power scaling of high power fiber laser. According to the power transfer equations, SRS effect in high power Yb3+ doped double clad fiber laser is studied. The effect of core diameter, fiber length, doped concentration and pumping method on the characteristic of fiber laser is studied. The way for suppressing SRS, such as increasing core diameter, decreasing fiber length, reducing doped concentration and using reasonable pumping method, is discussed. The theoretical model is proved by the experimental result.