The utility model discloses a self-closing water feeding valve of a solar water heater. The valve comprises a floating ball (1) and a piston (5), wherein the floating ball (1) and the piston (5) of a housing are positioned in an inner cavity of the housing; an air exhaust pipe (3) and a water inlet-outlet pipe (4) of a water box, which are communicated with the water box (8) of the solar water heater up and down, are arranged on one side of the housing (7); a water inlet-outlet (6) is formed on the other side of the housing; and the piston (5) positioned between the water inlet-outlet pipe (4) of the water box and the water inlet-outlet (6) is connected with the floating ball (1) through a connecting rod (2). The valve can automatically stop water feeding after the solar water heater is full of water, thereby dispensing with personnel watching during water feeding and avoiding water resource waste.