In order to solve the problem that current sampling characteristics of EVCT and MU cannot fulfill the practical demand of power quality analysis such as high-frequency harmonics and voltage transients in digital substations, this paper proposes a new power quality monitoring (PQM) system for digital substation with high sampling rate of 512 points / cycle. By use of new high-sampling-rated EVCT, MU and PQM equipment, the problem of low sampling rate is solved from the beginning of EVCT in process level. Other problems such as retrieving data from both EVCT and traditional transformer, mass data processing derived from high sampling rate, IEC 61850 modeling of digital PQM equipment, automatic calibration of MU and PQM equipment are analyzed and solved at the same time. Calibration result shows that this system can meet the function and accuracy standard and practical application of this system has achieved good results.