An actuator includes a base, a stationary frame fixed on the base, a movable frame received in the stationary frame, a SMA line, a guide pole, a position sensor, and a controller. The movable frame includes a resisting surface adjacent to the base, and defines a hole. The SMA line resists on the resisting surface. Two ends of the SMA line are fixed on the stationary frame. The guide pole is fixed on the base and extends through the hole. The position sensor detects the position of the movable frame. The controller supplies current to heat the SMA line to change the length of the SMA line, the SMA line drives the movable frame to move along the guide pole accordingly. The controller adjusts the current according to the position of the movable frame detected by the position sensor.