At present, the equivalent transformer model obtains a wide range of applications in the calculation of multi-voltage power grid, but it also faces the problems of complicated computation, poor adaptability, not conducive to analysis and programming when taking into account the effect of tap changer regulation on transformer equivalent impedance. The equivalent transformer model based on CIM can easily consider the effect of tap changer regulation on transformer equivalent impedance. The model is simple, easy to grasp and use, greatly improving the computational efficiency and helps the real-time computing of power system. The model is proved to be accurate, simple and convenient according to the comparative analysis of a numerical example given in this paper.