The sky cleaner 3 is shown in Fig. A turning waist joint actuated by a pendulum cylinder connects the X and Y cylinders. On opposite ends in the Y direction there are also four brush cylinders, which actuate the brushes up and down. An adaptive cleaning head is designed especially for effective, efficient and safe cleaning, equipped with a drainage collecting device. When the glass is being cleaned, the water is not allowed to drip down; it is firstly drawn off the glass wall through a vacuum pump on the robot. Then the water will flow down because of the gravity and be collected on the supporting vehicle on the ground. At last the drainage will be filtered, and then reused for cleaning. Some sensors that can detect the window obstacles are mounted on each end of the X and Y cylinders. The robot can both clean and walk on the glass walls automatically in the up-down direction as well as the right-left direction.