Abstract: In order to carry out the power combination by using phase locking for the L band magnetrons, it is necessary to understand the process of phase locking for one magnetron. This paper uses a injection phase locking methode which is putting a signal into the magnetron. Phase locking condition of the magnetron are discussed and numerical analysis. Having a simulation to the process of phase locking by using three-dimensional Particle-in-cell simulation code, Magic_3D. The result shows, when the frequency diffrence of the L band magnetron and injection signal is 0.3MHz and injection ratio is 0.248, the magnetron can achieve phase locking, besides, the output energy of phase locking is 19.2KW, the efficiency is 70%.