Abstract: We analyze the synchronous self-locking of metronomes and gave its physical explanation. The pendulum is in vibration damping after captured by escapement of metronome and in the meantime，all metronomes are weakly coupled by the vibration，resulting in the vibration phase shift backward than the former one and shift forward than the latter one. Finally，all the vibration of metronome is synchronous.

Key words: metronome, physical pendulum, vibration damping, weak coupling, vibration phase