Abstract: The measurement accuracy of low-voltage current transformer for distribution network directly affects the safe, stable and economic operation of distribution network, so it is necessary to grasp its operation status in real time. In the on-line calibration method of digital comparison method, the standard channel analog-to-digital converter in the analog-to-digital conversion process has a fixed delay and is difficult to fully compensate. Aiming at this problem, a Hilbert precise phase shift algorithm based on time series-weighted correlation degree extension combined with 4-term 3-derivative Nuttall window is proposed, which effectively suppresses the′end effect′ and realizes the precise phase shift of the fixed delay of the analog-to-digital converter. The simulation results show that the phase shift deviation of the algorithm is less than 10^-10 under the interference of frequency offset, harmonics and noise. On this basis, an on-line calibration device is developed. The ratio error between the device and the off-line calibration device is less than 0.006%, which can meet the requirements of on-line calibration for 0.2S-accuracy low-voltage current transformer for distribution network.