The invention discloses a cleaning device for the roof of a greenhouse. The cleaning device comprises a water spraying device, a cleaning working belt and walking devices, wherein the water spraying device comprises a water supplying pipe and a water spraying part; water spraying holes are formed in one side, close to the roof, of the water spraying part, so that water is sprayed on the surface of the roof; the water spraying part is a base body with a hollow structure; and the base body is a pipe-shaped component with an annular structure; the base body is provided with a first side surface and a second side surface which are opposite to each other; a first water spraying part is arranged on the first side surface; a second water spraying part is arranged on the second side surface; the base body naturally clings to the roof, and is connected with two ends in the length direction of the cleaning working belt; the walking devices are provided with power devices and are separately arranged on gutters on two sides of the roof of the greenhouse; and the walking devices are connected with two ends in the length direction of the cleaning working belt and drive the cleaning working belt to scrub the surface of the roof of the greenhouse repeatedly in the width direction.