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With the progress of Global Navigation Satellite System(GNSS),which mainly include GPS,GLONASS,GALILEO as well as BeiDou,multi‐GNSS joint working mode has become a development and application trend.The System time offset between two satellite navigation systems is one of the most important aspects of their interoperability and compatibility.This paper introduces the research progress of GNSS System Time Offset Monitoring and prediction at NTSC.The reasons that GNSS system time offset monitoring is done by means of Signal‐in‐Space Reception are analyzed and the measurement principle is discussed in detail.Multi‐GNSS receiver calibration is the key technology of GNSS system time offset monitoring with Signal‐in‐Space Reception.The causes of Inter‐System biases and inter‐frequency biases are researched and so does their calibration method.The calibration results are showed and analyzed.The key technologies of BDs system time offset monitoring are researched which include the algorithms related to satellite equipment group delay and dual‐frequency ionosphere delay correction whose measurement result is illustrated.And then,the system time offset monitoring results of UTC(NTSC)‐GPST and UTC(NTSC)‐GLONASST by Signal‐in‐Space Reception for six months long are showed and their precisions is up to 2.10ns and 3.24ns respectively.Furthermore,the experiment results about BDS system time offset UTC(NTSC)‐BDT calculated from all visible BDs satellites from 1 to 12 are displayed.Finally,the intentional application and development directions of GNSS system time offset monitoring are put forward.