Because the simple beam of traditional equal section used for tuning fiber Bragg grating (FBG) can make the FBG produce chirp, a novel tuning structure utilizing the equilateral rhombic beam under pure bending is designed, which has no chirp appearing. The experimental research is consistent with theoretical research well. The novel rhombic beam can realize the tuning wavelength of 8 nm, the linearity of 99.9%. And the 3 dB reflection bandwidth shows no change during the tuning process. The beam under pure bending has good symmetry, which realizes the linearly chirp-free central wavelength tuning of FBG.<网络出版日期:>2015-12-18