An electronic parking brake system and assistant starting method thereof for a motor vehicle are provided, wherein, the electronic parking brake system receives all sensor signals and detection signals of the motor vehicle; when any one of the following conditions is satisfied, the brake will be released to assist the driver in starting: condition (1): a torque T c transmitted by a clutch is calculated, and the calculated torque T c transmitted by the clutch is greater than a torque needed for starting the motor vehicle; condition (2): an engine rotate speed is greater than an engine idle speed, and an accelerator pedal and a clutch pedal are depressed simultaneously; condition (3): starting trend of the motor vehicle is detected; condition (4): the detected engine rotate speed is lower than a first predetermined threshold value calculated according to a throttle opening data; condition (5): a detected rotate speed or angle of driving wheel is greater than a predetermined threshold value of rotate speed or angle. In the application of the electronic parking brake system and assistant starting method thereof for a motor vehicle, there is no need to additionally a mount clutch position sensor and a gear position sensor; according to all the available sensor signals and detection signals on the motor vehicle, the system can accurately judge whether the brake can be automatically released, and there is no need to modify the existing motor vehicle, featuring low lost and accurate judgment.