In order to explore the influence of different outer coatings on sensing performance, a photonic crystal fiber (PCF)refractive index sensing structure based on surface plasmon resonance(SPR) is designed in this paper, the outer surface of the optical fiber is coated with a metal film. Through finite element method, the effects of coating materials are gold, silver, graphene and silver+zinc oxideon the sensing performance have been compared. Numerical studies show that when the structural parameters are the same, in the refractive index range of 1.33~1.38, the sensitivity of the sensing structure with graphene as coating material is higher, up to 7000 nm/RIU, gold as coating material is 5000 nm/RIU, silver and silver + ZnO as coating material are both 4000 nm/RIU; In terms of sensitivity fitting linearity, each coating has high linearity, and the linearity of silver coating is the highest, which can reach 0.99112.