Surface plasmon resonance is a label-free sensing technology. When the dielectric constant around the medium changes, the SPR resonance spectral characteristics will also change. Because the titanium dioxide (TiO₂) covering layer can completely protect the metal layer, it can be converted into a 1 550 nm optical fiber sensor through the spectral intensity and reflection wavelength of SPR reflection at the near-infrared wavelength, and its redox reaction can also realize the effective use of detection gas. Due to the flammability and explosiveness of turbines and the wide application of converted hydrogen energy, it has special significance for researching low-concentration gas-phase detection technology. This paper proposes a replaceable silver/titanium dioxide composite film surface. Plasma resonance gas sensor studied the SPR sensor near 1 550 nm. Surface plasmon resonance spectral characteristics. The relationship between the resonance spectrum intensity of the four-layer structure model coupled with the Kretschmann prism and the thickness of the silver film, the thickness of titanium dioxide and the prism material was calculated by simulation, and the maximum sensitivity of the thickness of Ag and TiO₂ layers were optimized. The best film thicknesses obtained were 45 nm Ag and 110 nm TiO₂. The Ag/TiO₂ film is designed as a replaceable one-time gas-sensitive film coated by evaporation and sputtering methods to prepare the SPR sensor used in this article. The Ag/TiO₂ film is used to generate the SP resonance spectrum shift at the composite interface to test the gas. Spectral wavelength detection experimental system using Kretschmann refractive index conversion structure. Fix the light source and the incident angle, and measure the displacement of the wavelength. The 1 550 nm wide light source (wavelength range: 1 462~1 662 nm) is irradiated to the prism coating and the replaceable Ag/TiO₂ sensitive film through the circulator and collimator. It then is reflected by the high reflector after the total reflection (TIR) The sensing film is reflected to the collimator again with the same TIR angle and light path, to be detected by the spectrometer. Experimental results show that the Ag/TiO₂ composite film can convert the resonance wavelength to 1 550 nm near-infrared spectrum, enhancing the sensor’s spectral sensitivity, and the sensitivity under low concentration (14.7%~25%) microns can reach -8.305 nm·%^-1. Moreover, it can detect different gases by replacing the gas-sensitive membrane with increasing biocompatibility and gas sensing capabilities.