It is suggested in this paper that the simple beam and the cantilever beam used for tuning FBG will make the FBG chirping. A novel tuning method utilizing the beam under pure bending is introduced. It is proved experimentally and theoretically that this new method will tune the Bragg wavelength without chirp. The FBG external cavity semiconductor laser using this new method has achieved the tuning wavelength of ±1 nm continuously and steadily.