The present disclosure provides a battery management system and a communication method. The method includes: determining, by a main BMU, from a plurality of managed units a fault unit that communicates abnormally with the main BMU, and transmitting, by the main BMU, to a backup BMU a fault frequency at which the fault unit communicates abnormally with the main BMU; selecting, by the backup BMU, from the managed units a managed unit that communicates normally with the backup BMU and the fault unit as a target unit; transmitting, by the backup BMU, frequency-conversion information to the fault unit through the target unit based on the fault frequency; converting, by the fault unit, its frequency to a frequency; transmitting the frequency to the main BMU if the backup BMU communicates normally with the fault unit using the frequency; and communicating, by the main BMU, with the fault unit using the frequency.