In this paper, a dual optimized down taper structure based on fiber Mach-Zehnder interferometer is designed. This structure is manufactured by using insufficient arc discharge splicing between single-mode fiber and polarization-maintaining fiber method, achieving simultaneous measurement of strain and temperature. The spherical core which located at the middle of the down taper can further regulate the light power distribution in the core and cladding area. The optimized structure can obtain a larger interference fringe extinction ratio of 16 dB, which is greater than the dual-down taper structure under the same parameters. Sensing experiments show that the proposed structure has high resolutions of ±1.616 με and ±0.79℃ in the range of 0~244.35 με and 25~50℃, respectively. The measurement error of both parameters is less than 1×10^-3% due to cross-sensitivity. This structure provides a promising method for simultaneous measurement of strain and temperature, which can be applied to precision instrument measurement.