A microfiber strain sensor with arched transition region was demonstrated. By controlling the flame size and tapering speed, a novel micro fiber with arched transition region was successfully fabricated. Consid-erable high order propagation modes of microfiber were excited by the arched transition region, resulting in in-creasing the depth of valley in the transmission spectrum of microfiber. The depth of the transmission valley is up to 18dB. Furthermore, when the axial strain increased, the position of the transmission valley was blue shift, the linearity is 99.15% and the axial strain sensitivity was -13.1 pm/με, which was one order magnitude larger than that of traditional fiber strain sensors based on Bragg grating. This kind of microfiber with arched transition region has many advantages, such as high sensitivity, good mechanical performance, compatibility to traditional optical fiber systems, and easy to be fabricated. It can be widely used in various physical, chemical and biological sens-ing and detection fields.