The invention relates to a clock synchronization system and method and belongs to the technical field of geophysical exploration, in particular to a VSP measurement clock synchronization system and method. The system comprises a ground synchronization device, an underground synchronization device, and a seismic source synchronization device. According to the invention, the starting and stopping of downhole instruments are controlled through the synchronous starting or ending signals emitted in every complete second. The recorded time at downhole is based on the ground time for the elimination of the time error. The system and method of the invention can correct the timing error of a VSP clock caused by the long-term poor stability due to the high temperature environment in the downhole through the delivery of accurate clock signals on the ground to the downhole by a time-sharing data carrying device.