Reducing the strain sensitivity of fiber Bragg grating (FBG) strain sensor is one important method to solve issues of small measurement range and undetectable large strain. In order to monitor stress and strain changes of components during use, one composite technology of spiral and slant gratings is proposed. The theoretical relationship between the measured strain by FBG and the actual strain of specimen is established. The measurement experiment of the grating strain sensitivity under different spiral-slant angles is done. The experimental results show that the proposed method can effectively reduce the strain sensitivity of FBG and increase the strain measurement range of FBG.