The invention discloses an electric water ball toy gun. The electric water ball toy gun comprises a cartridge receiver, an electric gearbox and a gun barrel, and further comprises a split ball supplytee joint, an upper ball supply type electric magazine, a fishbone expansion device, an overturning-closing cartridge receiver cover, a gunstock and an upper cover, wherein two ports of the split ballsupply tee joint are matched with the electric gearbox and the gun barrel respectively, the upper ball supply type electric magazine is matched with a third port of the split ball supply tee joint, the fishbone expansion device is assembled outside the gun barrel, the overturning-closing cartridge receiver cover is connected with the fishbone expansion device and is matched with the cartridge receiver, and the gunstock is provided with a core-supporting battery compartment; and the split ball supply tee joint comprises a base and an upper cover, wherein the base is provided with a transverselower half groove and a longitudinal ball supply channel communicating with the transverse lower half groove, the longitudinal ball supply channel is connected with the upper ball supply type electricmagazine, the upper cover is detachably connected with the base, a transverse upper half groove matched with the transverse lower half groove is formed in the upper cover, the transverse upper half groove and the transverse lower half groove are in butt joint to form a transverse ball supply channel, and the two ends of the transverse ball supply channel are connected with an inner tube of the gun barrel and a ball pushing nozzle of the electric gearbox respectively. The water ball toy gun can prevent refitting and is high in safety.