Disclosed is an automatic switching delaying water-saving flush valve, which mainly comprises a pedal mechanism (1), a water valve (2), a valve core (3) and a mounting base (4), wherein the pedal mechanism (1) controls a valve core shaft (31) which is strung with an upper water sealing piston (32) and a lower water sealing piston (33), under actions of a panel return spring (14) and a water sealing piston return spring (36), the valve core shaft (31) can move up and down, then water sealing and unsealing processes can be completed by the upper water sealing piston (32) and the lower water sealing piston (33) alternately, thereby realizing the process of automatic switching and delayed flushing of the flush valve. The automatic switching delaying water-saving flush valve has simple structure, reliable working, low manufacturing cost and simple use and maintenance.