In this paper, we study the spin Hall effect (SHE) of light in a multilayer-medium. By taking three-layer medium for example, the three-dimensional transmission model of beams passing through a prim-air-prim barrier is build. The various factors in SHE of light, such as thickness of the air gap, refractive index gradient, and incidence angle are investigated. For a certain circularly polarized component, the transverse shift can be modulated by Changing the refractive index gradient associated with the two prisms: whether the transverse shift of reflection and transmission fields is positive or negative depends on the refractive index gradient. Compared with the SHE in the two-layer medium, the SHE in the Gaussian beam refraction can be evidently enhanced via three-layer medium. Based on the theory of SHE of light,the theoretical basis for regulating and enhancing optical spin Hall effect is obtained.