Abstract: In order to solve the problems of small free spectrum range or low interference fringe fineness, a strain sensing structure and its improved scheme of Fabry-Perot cavity based on single tapered fiber Bragg grating was proposed. By utilizing the characteristic of reflecting different wavelengths at different positions of the chirped fiber Bragg grating, the Fabry-Perot cavity was formed with a continuous variation of cavity length with wavelength, and the infinitely-great free spectrum range as well as the high resonance valley fineness was obtained. Numerical results show that the strain sensing sensitivity is positively related with the lumbar region diameter and grating region length of tapered fiber. In the range of 0~300 με, the strain sensing sensitivity is obtained to be 7.05 pm/με when the lumbar region diameter is 3/25 of the fiber diameter and the grating region length is 30 mm. The results have some reference value for the design of other interferometric sensing structures.