A control method of restarting an engine of an AT ISG vehicle may include a first step of restarting the engine when a state of the vehicle satisfies a restart condition after an idle-stop, a second step of keeping a throttle valve constant at a first critical value or less when a positional value of an acceleration pedal may be equal to a second critical value or more after the first step, and a third step of opening a throttle valve until the positional value of the acceleration pedal detected by the acceleration pedal position sensor and a positional value of the throttle valve detected by a throttle valve position sensor may be matched after a critical time passes, a shifting may be completed after the restarting, or when the acceleration pedal may be pressed down less than at the second critical value after the first step.