The invention relates to a water-saving automatic irrigation and drainage system for a green belt. The water-saving automatic irrigation and drainage system comprises a water storage pond, a water inlet channel, a drainage channel, a silt discharging channel, a sponge water absorbing mat and fiber water absorbing bars. The water storage pond is arranged in a stratum below a bottom plate of the green belt and located on an urban sewer, the upper end of the side wall of the water storage pond makes contact with the bottom plate of the green belt, the bottom plate of the green belt serves as a cover plate, downflow weirs are arranged on the upper portions of the two side walls of the water storage pond in the length direction of the green belt, silt discharging holes are formed in the lower portions of the two side walls, an automatic flap gate matched with each silt discharging hole is installed on an orifice of the silt discharging hole to close or open the silt discharging hole, and multiple through holes are uniformly distributed in the bottom plate of the green belt. The adverse affect on green belt plant irrigation caused when the water level of a water collecting system is too high or low can be eliminated, the structure is simplified, and it is avoided that the system is blocked due to sediment accumulation.