The axial strain of D-shaped fiber Bragg grating (D-FBG) and normal fiber Bragg grating induced by bending was analyzed with mechanics of materials. Bending sensitivity characteristic of Bragg wavelength's shift was obtained. Experiment result was in good agreement with the theory analysis. DFBG's bending sensitivity was about 80 times higher than normal circularly symmetrical FBG. The studied D-FBG can be directly applied in bending measurement,and indirectly in pressure or acceleration measurement. The theory analysis and experiment result was helpful for the design of device or sensor system using D-FBG.