Abstract: Catalytic cracking is the main method to lighten heavy crude oil, this process can produce high quality oil products such as gasoline and diesel, but also produces a large amount of fluid catalytic cracking slurry (FCCS). The catalyst particles in FCCS seriously restrict the secondary processing of FCCS and need to be removed, and the properties of FCCS is an important factor that affects the removal efficiency of the catalyst particles. Based on the “effective contact point” model proposed by the research group, this study further proposed the “electrostatic separation efficiency calculation” model. In this model, since FCCS has a uniform distribution of catalyst particles, the ratio of the number of catalyst particles can be expressed as the ratio of area to achieve the calculation of separation efficiency. Then the catalyst removal efficiency under different viscosity was analyzed, thus verifying the feasibility of this model. The effects of temperature and mass ratio of four components on the viscosity of FCCS were investigated respectively, then the effects of temperature and four components’ mass ratio on the electrostatic separation can be directly converted into the effect of viscosity on the electrostatic separation efficiency. All the results show the electrostatic separation efficiency decreases with increasing viscosity, and the best separation temperature is 120 °C.