GNSS has the capability of time transfer. The technologies used for the time transfer include time transfer of precise point positioning, time transfer using common view method, relative time synchronization with DGNSS. The methods are used to achieve high precise time synchronization between fixed station and mobile platform of a typical distributing system. By analyzing the principle and capability of several GNSS time transfer modes, the paper gives a comparison and analysis of the time transfer capability of GPS, GLONASS, GALILEO and Compass. Two sets of time transfer systems using carrier phase time transfer technology of multiple systems and multiple satellites’ common view are used to make an experiment of long baseline time transfer. The result shows that the precision of the carrier-phase time transfer using all the satellites’ common-view is less than 5ns within 1000km of long baseline.