Abstract: In order to solve the problems of low frequency noise,voltage drift and the measurement accuracy in the integral part of the electronic current transformer measurement and improve the engineering practicability of air-core coil electronic current transformer,an improved high-precision digital integral algorithm is proposed based on the principle of variable step integral algorithm.Compared to some other improved integral transfer functions,the error of the frequency characteristic and the ideal integral is much smaller.Meanwhile,the algorithm has the advantages of moderate sampling rate,less amount of calculation and high precision.The simulation results show that the improved algorithm has good performance and better ability of resisting noise and voltage drift.