An internal engagement structure of a housing for a water control valve, the water control valve including the housing and a valve assembly, and the housing contains: a holder and a cover. The holder is configured to accommodate the valve assembly, and the cover is covered on the holder. The holder includes two opposite receiving grooves, two locking recesses formed on two lower ends of the two opposite receiving grooves respectively and communicating with the holder, and two tilted guide faces arranged on two upper ends of the two opposite receiving grooves respectively. The cover includes two opposite retainers extending downward from a bottom thereof and corresponding to the two opposite receiving grooves respectively, two hooks formed on two lower ends of the two opposite retainers respectively, and two cutouts defined above the two hooks respectively and configured to accommodate the two tilted guide faces respectively.