In an integrated ion trap with integrated optical modules, the problem of misalignment between the optical focus and the trapped ion saddle point is very likely to occur, which seriously hinders the practicality of the experimental method. To solve this problem, the multi-RF field method can be used to compensate for and move the ion saddle point position. However, in the actual experimental process, the application of the multi-RF method requires the knowledge of the amplitude of the RF voltage to be loaded corresponding to the actual spatial position of the saddle point. Therefore, a set of mathematical models is established to describe the relationship. The accuracy of the model determines the control accuracy of the spatial position of the saddle point, and the simplicity of the model determines the speed of the solution process. Therefore, in this work, a mathematical model of the relationship between the multi-RF electric field voltage and the saddle point position is proposed based on the numerically simulated electric field distribution and the polynomial fitting method. It can quickly and accurately give a mathematical description between the two without considering the physical mechanism or model. Numerical method is adopted to verify and discuss the correctness and scope of application of the model, and can quickly and accurately provide the amplitude of the RF voltage to be loaded in the experiment, causing the saddle point to move and coincide with the optical focus. This method greatly reduces the time delay caused by the solution and improves the feedback loop bandwidth during the movement of the saddle point position.