In this paper, a silicon-based Mach-Zehnder interferometer (MZI) refractive index sensor working in the near infrared band is designed. Theoretical and simulation analysis show that the dispersion turning characteristics of the output interference spectrum can be regulated by changing the structural parameters of MZI. After optimization, the wavelength corresponding to the dispersion turning point (DTP) can be adjusted to the near-infrared band (1550 nm). By changing the ambient refractive index (SRI) around the MZI, the refractive index sensitivity can reach 37500 nm/RIU. Since the interference fringes on both sides of DTP have opposite characteristics to the refractive index response of the outside world, taking the relative drift of the interference trough as the detection object can improve the sensitivity by two times, the value is 75000 nm/RIU. Different from conventional DTP sensor based on grating and waveguide coupling structure, the two interference modes in the designed DTP structure are unrelated and can be adjusted independently, and the dispersion transition wavelength can be adjusted flexibly according to the needs.