Abstract: Double-clad scheme has provided an effective solution to take use of high power semiconductor lasers(or laser arrays) as the pump source.However,with the increase of the fiber laser power,stimulated Raman scattering may reach its threshold and finally limit the further increase of the fiber laser powers.After adopting justified approximation,it was analytically solved.The rate equation of the double-clad fiber lasers without the spontaneous emission terms,and expressions for the fiber laser power and pump power were derived when the Stokes radiation inside fiber reached its threshold.Based on these expressions,dependence of the threshold on the fiber laser parameters were studied.