The frequency hopping technology can be used to avoid the frequency-selective attenuation and narrow-band interferences of 10kV power line communication channel. In the frequency-hopping communication system, it always goes through a process of frequency locking. The paper analyzes the lock time of phase-locked loop (PLL) when the initial frequencies of reference signal and the output of voltage-controlled oscillator are different. In order to shorten the lock time, a novel method is proposed by adding a DC tuning voltage. And the simulation results show that this method is effective to speed up the lock process. At last, the scheme of PLL frequency synthesizer is presented which is fit for the power line communication system using frequency hopping.