A novel fiber curvature sensor based on modal interferometer with waist-enlarge splicing is proposed. A section of 30mm polarization maintaining fiber (PMF) is spliced with waist enlarge between two conventional single mode fibers (SMFs) to construct an all fiber curvature sensor. The results show that the transmission spectrum has a blue and red shift, corresponding to the opposite curvature directions. The sensitivity coefficient of −10.634nm/m −1 and 10.152nm/m −1 were acquired by concave and convex bending with the range from 0m −1 to 2.054m −1 , and the corresponding resolution were 9.4×10 −4 m −1 and 9.85×10 −4 m −1 , respectively. And the influence of different lengths of PMF on the sensitivity was also discussed.