An apparatus for controlling a start of an engine may include the engine, a first motor connected to a crankshaft by a first connecting device to start the engine, a main battery supplying a start power to the first motor, a controller configured to monitor components of a vehicle according to a start command for the engine to generate diagnostic information and generating a reverse charging control command to supply the reverse charging power to the main battery as the determination result of the diagnostic information, and an auxiliary battery supplying the reverse charging power to the main battery according to the reverse charging control command.