Seismic Synchronous acquisition means the Field Digitizer Unit acquiring data of each geophone at the same time. Here we will present a method to realize synchronous data acquisition of which the synchronous process is finished at FDU. A timer will be used to precisely measure the time difference between data transmission in positive direction and that in negative direction. And then work out the delayed time needed by each FDU. In that way, when receiving the command to acquire data synchronously again, the delay time control AD transformation can be well dealt with, so as to realize the purpose of synchronous resetting and acquisition. Through hardware circuit test, the two power stations have 15 FDU and each station is 25m or 50m apart, Accuracy of synchronization at each acquisition station reach 200ns. Besides, this method can be used for reference for technology of synchronization of other serial acquisition systems.