Based on an analysis of the errors for a clock and by taking into account the characteristic that the GPS second clock is free from cumulative errors and the crystal oscillator clock is free from random errors， a new method is proposed to implement the highly accurate clock by the synchronization of a crystal oscillator second clock with GPS second clock. According to the digital phase-lock principle， the method is used to control the frequency dividing coefficient by measuring the actual phase difference between the crystal oscillator second clock and the one pulse per second（1PPS） of GPS to eliminate the cumulative errors of the crystal oscillator second clock in real time， thereby generating the high accuracy second clock. Experimental results show， when the GPS receiver works normally， that the synchronous second clock accuracy can be maintained at 20 ns， while if the GPS signal becomes ineffective for one hour， the accuracy of the synchronous second clock can still be stabilized at 100 ns. A high accuracy clock generating device with a fairly high price performance ratio has been developed using this method and successfully applied in a traveling wave locating system.