Automatic irrigation system for greenhouse

The invention discloses an automatic irrigation system for a greenhouse, which belongs to the technical field of irrigation and comprises a spraying support, a water supply pipe and a watering assembly. The water supply pipe is installed on the spraying support, and the water spraying assembly comprises a spraying head, an installation ring, a water pressure shifting block, a sliding strip and an elastic piece. The sprinkling assembly in the greenhouse automatic irrigation system can automatically adjust the orientation of the nozzles and whether the nozzles are communicated with the water supply pipe or not according to water pressure, when the pressure in the water supply pipe is large, the nozzles can rotate to be communicated with the water supply pipe through control of the water pressure shifting block and the mounting ring, and therefore sprinkling operation is conducted; when water supply to the water supply pipe is stopped, the water pressure in the water supply pipe is gradually reduced, at the mome