A method for charging a battery module including a plurality of parallelly-connected battery cell sets in multiple stages is provided. In the present invention, a constant current charging is applied for charging the battery module in an initial stage of charging through the method of voltage control or current control. Then, the charging current is lowered substantially to reduce the charging speed when the voltage of one of the battery cell sets exceeds a safety value or a total voltage of the battery module itself reaches a rated voltage. Accordingly, a safety problem of the battery can be avoided and battery life can be prolonged.