The invention relates to a DC power transmission system bipolar VSC passive control method and device. One pole of VSC of an inversion side is controlled to be unlocked and then controlled by using constant AC voltage, then the other pole of VSC of the inversion side is controlled to lock the output phase of one pole of VSC and the other pole of VSC is controlled to be unlocked after phase locking. Smooth unlocking of the bipolar VSC can be realized, and the voltage phase of the bipolar VSC can be maintained to be synchronous after unlocking and stably supplies power to the same passive network.