Abstract: In order to measure and detect refractive index of solution, by using transfer matrix method, the coupling system of Ce:YIG/Ag/liquid three-layer structure and prism based on magneto optic surface plasma resonance was studied. Numerical calculation was carried out and finite element method was used to simulate. For the structure composed of low loss Ag and strong magneto optical Ce:YIG, its sensitivity is to 4.082/RIU, solution refractive index is 1.330~1.340 when incident light wavelength is 980nm. The results show that compared with other conventional surface plasma resonance sensing structures, the sensitivity of the refractive index sensor presented in this paper is greatly improved. The structure can be used to detect refractive index of the solution more easily.