Weak-light phase locking is a key technology for Taiji space gravitational wave detection and its pathfinder mission. Previously, the phase locking was achieved by a complicated technique, which controls the frequency of the laser via a piezo-electric actuator (kHz range or more) and a temperature actuator (sub-Hz range). We propose an easy phase-locking strategy, which is based on the electro-optic modulator (EOM). Compared with the traditional way, this strategy only needs to modulate the driven voltage of the EOM, and the frequency bandwidth can cover all ranges. An experiment is also established to prove the feasibility of the method. The results show that the noises are <80 mu rad/Hz(1/2) in frequencies from 0.2 to 1 Hz, and the thermal drift is the main noise source in our recent system. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)