Stimulated Raman Scattering (SRS) is the primary restrictive factor in the improvement of output power and stability of high-power fiber laser. Effective filtering and suppressing of SRS are a key dilemma that need resolution. To effectively filter the Stokes light caused by SRS, long period fiber grating (LPFG) can couple core mode with special wavelength to cladding modes to realize bandwidth filtering. Hence, the CO₂ laser beam combined with scanning galvanometer is used to fabricate LPFG on double cladding fiber to filter and suppress Raman signal in high-power optical fiber oscillator and an evident inhibition is achieved. Results show that the filtering ratio of Stokes light beyond 15 dB, the purity of signal laser and stability of the system have improved considerably. Because there is no effect on fiber core, theoretically, the proposed method has a very low signal optical transmission loss, which is of great value in high-power fiber laser.