The wiper assembly includes motor, reducer, four-bar linkage, wiper arm spindle, wiper blade assembly, etc. When the driver presses the switch of the windscreen wiper, the motor starts, the speed of the motor drives the swing arm through the deceleration and torsion increasing action of the worm, the swing arm drives the four-bar mechanism, the four-bar mechanism drives the rotating shaft installed on the front panel to swing left and right, and finally the rotating shaft drives the wiper blade to sweep the windshield