Provided is a starting method for hybrid electric vehicle, which includes the steps of: (a1) as the temperature of a battery module of the hybrid electric vehicle is below a first threshold temperature, allowing the vehicle control unit of the hybrid electric vehicle to turn on a first switch; (a2) converting the DC power transmitted from the battery module to an integrated starter generator of the vehicle through the first switch into a first AC power by the integrated starter generator which is operating under the starter mode, and starting the internal combustion engine of the vehicle with the first AC power; and (a3) executing a heating process to warm up the battery module by a battery heater, in which the charging line between the integrated starter generator and the battery module is cut off and the integrated starter generator is operating under a rectifier sub-mode, thereby allowing the integrated starter generator to supply electric power to the battery heater in order to heat the battery module.