A washing machine for automatically adding the detergent by negative pressure comprises a water inlet, a detergent container and a tub. A main inflow waterway and a rinse waterway are provided between the water inlet and the tub. A dosing container which communicates with the detergent container is provided between the rinse waterway and the tub. A venturi tube is provided in the main inflow waterway. Due to venturi effect, the main inflow water stream becomes narrower and the water inflowing velocity is accelerated, so that a relative vacuum area which communicates with the dosing container is formed at the rear side of the venturi tube outlet, negative pressure is generated in the dosing container, and the detergent in the detergent container.