In this paper, we demonstrate a narrow linewidth random fiber laser (RDFL), which employed a narrow-band fiber Bragg grating (FBG) to construct a half-open cavity and function as filtering element. Spectral linewidth down to 40 GHz has been measured. The maximum output power reaches 2.15 W at 1081.4 nm when 8.97 W pump light centered at 1036.5 nm is launched into the half-open cavity, which is more powerful than the previous reported results with ~100 mW output power.