The embodiment of the invention discloses an automatic addressing method and device of an electric vehicle battery management system. The electric vehicle battery management system comprises at least two slave control modules and a master control module; and the method comprises the steps as follows: a pulse width modulation signal line of one slave control module is connected with the pulse width modulation signal line of the master control module in series and the pulse width modulation signal lines of the other slave control modules are gradually connected in series from the slave control module; the master control module transmits pulse width modulation signals of which the duty ratios are preset values to the slave control modules which are connected with the master control module in series; and each slave control module sets an encoded address itself on the basis of the duty ratio included in the received pulse width modulation signal, and each slave control module increases a predetermined step value to the duty ratio included in the received pulse width modulation signal and transmits the pulse width modulation signal with the increased predetermined step value to the slave control module which is connected with the slave control module in series. According to the automatic addressing method and device, incremental automatic addressing is achieved and the workload and the error probability are reduced.