In order to explore the effect of titanium dioxide (TiO₂)/poly(sodium 4-styrenesulfonate) (PSS) nanofilms on the Kretschmann-type surface plasmon resonance sensor, the spectral changes of the sensor after depositing TiO₂/PSS nanofilms of different thicknesses were systematically studied. The reasons for the spectral changes were further explained and discussed theoretically. First, TiO₂/PSS multilayer films were deposited in situ on the surface of the glass chip sputtered with a gold layer via electrostatic layer-by-layer self-assembly technology, and the corresponding reflection spectra of the sensor were recorded in real time. Then, the original reflectance spectrum data was processed to make the spectral curve clearer and more visible. Finally, the experimental results were simulated and analyzed using MATLAB software programming. The results show that with the number of TiO₂/PSS bilayers increasing, four different types of reflection peaks successively appeared in the sensor’s spectra in the 450-900 nm wavelength range. The four types of reflection peaks correspond to the surface plasmon resonance mode, the first-order mode, the second-order mode, and the third-order mode of the transverse magnetic mode of the sensor, respectively. This indicates that the Kretschmann-type sensor’s sensing mode and reflection spectrum type can be modulated by controlling the thickness of TiO₂/PSS thin films.