An electric power assist device and a driving method for an electric vehicle are provided. The electric power assist device adapted for the electric vehicle includes an angle sensing unit, a driving module, and a control module. The angle sensing unit senses a tilting angle of the electric vehicle on the road. The driving module includes a power driving unit and a motor. The driving module receives a control signal for driving the electric vehicle by the motor. The control module is coupled to the angle sensing unit and the driving module. The control module adjusts the control signal according to a change of the tilting angle to increase a torque force of the motor when the electric vehicle is on an uphill road.
