In view of the common problems of fiber surface plasmon resonance sensor with weak strength, low sensitivity and low plasma excitation efficiency, this paper proposes to use the long-period fiber grating as an auxiliary platform to study the ways of enhancing the sensitivity of surface plasmon resonance sensors. A layer of gold film is thermally evaporated on the sensing area of the fiber grating surface, and the external sensing performance is enhanced by tuning the polarization mode of the input fiber grating. We choose the sodium chloride solution as the external refractive index sensing material, and conduct a simulation through software. The results show that before and after the gold coating, the transmission power of the transverse magnetic wave and the transverse electric wave are attenuated by 4.3 and 0.3 dB in the air, and 5.3 and 2.2 dB in the solution. Within the range of refractive index change of the solution from 1.335~1.372, the refractive index sensitivity of the two polarized light sources increased by 18.7 and 12.9 nm/RIU, respectively.