The present invention relates to an engine torque control method of a mild hybrid electric vehicle including an engine as a power source, the mild hybrid electric vehicle further includes a mild hybrid starter and generator (MHSG) which starts the engine or operates as a generator by an engine torque and a controller which controls the change of a fuel injection mode among a MPI engine mode using a low pressure injector which injects the fuel to an intake port of the engine, a GDI engine mode using a high pressure injector which injects a fuel to a combustion chamber of the engine, and a hybrid MPI and GDI engine mode using both the low pressure injector and the high pressure injector, and the engine torque control method includes: determining whether a fuel injection mode is a MPI engine mode, by the controller, measuring a maintaining period when the MPI engine mode is maintained by a timer when the fuel injection mode is the MPI engine mode, determining whether the fuel injection mode is changed from the MPI engine mode to the GDI engine mode or the hybrid MPI and GDI engine mode, by the controller; and, driving the MHSG by the controller to assist an engine torque when the fuel injection mode is changed from the MPI engine mode to the GDI engine mode or the hybrid MPI and GDI engine mode.