An apparatus and method for controlling cold starting of a mild hybrid vehicle, are disclosed. The method includes: measuring, by a sensor, a cooling water temperature of the vehicle when a request is received to start an engine; operating, by a controller, a starter to drive an engine when the cooling water temperature is less than a preset reference temperature, and stopping the operation of the starter and operating an MHSG to drive the engine when RPM of the engine driven by the starter exceeds a preset reference value. In particular, stepwise starting according to the cold starting of the vehicle is performed. The apparatus and the method are advantageous in that a starter and alternator are simultaneously controlled under a cold starting condition to provide startability and reduce capacity of a starter, reducing manufacturing costs.