The invention discloses a water-saving irrigation device. The device comprises an extension connector, a combined pipe, a first functional box, an auxiliary box, an oblique collecting plate, a collecting port, a closed rain box, a mixing box, a second functional box, supporting feet, a water outlet seat, a base, an irrigation pipe, oblique pipes, installation support plates, four-way adapters, a first conversion sleeve head, a straight cylinder pipe, a tail pipe, a sealing cover, long branch pipes, thin branch pipes, a spraying pipe and nozzle threaded seats. According to the water-saving irrigation device, by arranging the oblique collecting plate and the auxiliary box at the inlet of the closed rain box, the advantages are achieved that the oblique collecting plate can be closed after rainwater is collected and a large evaporation amount of the rainwater due to an open oblique collecting plate during daytime is avoided. By arranging the water outlet seat in the bottom of the mixing box, the advantages are achieved that the rainwater is autonomously transferred and the storage capacity is increased. By arranging the mixing box, the second functional box and the first functional box on the left side of the closed rain box, the advantages are achieved that nutrients can be mixed and added for irritation to save the time for subsequent manual operation of nutrient replenishment and the functionality is high.