The combination of nano-film and optical fiber provides various potentials for novel sensing. In order to analyze the formula design of the temperature-sensitive film and its influence on the sensing characteristics of the optical fiber temperature sensor. According to the theory of optical thin film and the temperature sensing principle of optical fiber sensor, the formla design of the sensitive thin film in the optical fiber temperature sensor is discussed, and the temperature sensing characteristic model of the thin film optical fiber sensor is constructed. Based on the parameters and performance of the test system and its requirements for the interference spectrum, a Fabry-Perot film cavity with good symmetry is designed. By comparing the sensing characteristics of Fabry-Perot formula with different film thicknesses, a formula is selected. The influence weights of the thermo-optic coefficient and thermal expansion coefficient of the high and low refractive index film materials on the temperature sensing characteristics are analyzed, which provides theoretical basis for the plating and process formulation of the temperature sensor sensitive thin film.