1. A method for controlling a mild hybrid electric vehicle, comprising steps of: detecting data regarding the mild hybrid electric vehicle; determining a target torque of an engine according to the detected data; determining whether knocking of the engine occurs according to the detected data; determining a retardation amount of an ignition timing when it is determined that the knocking occurs; comparing the retardation amount of the ignition timing with a value; determining a loss amount of a combustion torque of the engine according to the retardation amount of the ignition timing when the retardation amount of the ignition timing is equal to or greater than the value; determining a target torque of a mild hybrid starter & generator (MHSG) according to the target torque of the engine and the loss amount of the combustion torque of the engine; and operating the MHSG to generate the target torque of the MHSG.