This paper presents a calculationscheme of inrush current of high voltage built-in high impedance transformer which takes into account the nonlinear changes of remanence and excitation inductance. Firstly, the inrush current model of the high voltage built-in high impedance transformer is constructed, and its amplitude, attenuation and harmonic characteristics are deeply analyzed. Secondly, a simulation system for a high-voltage built-in high-impedance transformer that meets the engineering practice is built, the excitation inrush current model and its characteristics of transformer are explored, a simulation and engineering calculation method that can quickly and effectively calculate the excitation inrush current is proposed, and the peak value and attenuation time of the simulation and engineering calculation method are verified according to the waveform of the field recording diagram. This paper discusses and summarizes the excitation inrush current characteristics of high voltage built-in high impedance transformer under the influence of many factors, and provides a certain reference for operation strategy and protection setting optimization.