This invention is related to a method and an apparatus for choosing SOCi (State Of Charge based on current) or SOCv (State Of Charge based on voltage) as the SOC (State Of Charge) of a battery depending on a condition in a battery management system by using an equivalent circuit model. In this invention, a method for measuring SOC of a battery in a battery management system is characterized by comprising the steps of: obtaining voltage data and temperature by measuring the current, voltage and temperature of a battery; calculating SOCi by accumulating the current data; calculating open circuit voltage by using an equivalent circuit model which simply presents the current data, the voltage data and the battery through an electric circuit; calculating SOCv by using the temperature data and the open circuit voltage; and choosing at least one of the SOCi and the SOCv as SOC of the battery by using the SOCi and the SOCv based on the judgment on the current state of a vehicle for a certain time interval.