In order to enhance the working performance of existing temperature sensor and refractive index sensor of sub-wavelength waveguide, the design of ring regular octagon surface plasmon resonance sensor with sharp transmission peak, high sensitivity and high integration was proposed in this paper based on surface plasmon polaritons. The feasibility of using ethanol as a thermosensitive filler to establish a linear conversion relationship between temperature and effective refractive index was analyzed theoretically. The reason why the real part of effective refractive index changes abruptly with the change of waveguide width is also explained. The multimode interference coupled mode theory (MICMT) was used to fit and analyze the transmission peak of the sensor, and then the finite element methods (FEM) is used for simulation analysis. Results obtained by the theory of the MICMT are consistent very well with those from simulation. In order to obtain the optimal parameter setting of the ring regular octagon surface plasmon resonance sensor, various parameters of the sensor are simulated by FEM. It is found that increasing L and decreasing H will improve the sensitivity of the sensor, while decreasing parameter w can not only improve the amplitude of transmission peak, but also keep the sensitivity unchanged. This characteristic of parameter w greatly improves the robustness of the sensor. All kinds of physical phenomena in this paper are analyzed in detail. Firstly, the phenomenon of transmission peak displacement caused by parameter changes is explained through the analysis of magnetic field distribution, and then the phenomenon of inconsistent sensitivity of different transmission peaks is explained through photon energy formula. Compared with the previous structural design, the dual-purpose sensor has many advantages such as wide operating wavelength range, narrow full width at half maximum and easy to integrate. As a temperature sensor and refractive index sensor, its sensitivity was as high as 0.9 nm/℃ and 2400 nm/RIU. The study of this structure broke through the limitations of some traditional cavities, in order to provide a high- performance cavity selection for the micro-nano photon temperature and refractive index dual-purpose sensor based on the design of surface plasmon polaritons in the future.