The invention provides an ejection system, an oil return system of a water chilling unit, a control method and the water chilling unit, and relates to the technical field of oil return control. The ejection system comprises a first ejector, wherein the first ejector is provided with a first high-pressure inlet, a first mixing inlet and a first outlet, the first high-pressure inlet is used for introducing high-pressure gaseous refrigerant, and the first mixing inlet is used for introducing oil and liquid refrigerant mixed liquid; the first outlet is communicated with an oil tank through a firstbranch, and a first electromagnetic valve is arranged on the first branch; the first outlet is communicated with an air suction port of the compressor through a second branch, and a second electromagnetic valve is arranged on the second branch. When the guide vane opening degree is large and the impeller air suction capacity is high, the first electromagnetic valve is controlled to be opened to enable the first branch to be communicated, the second electromagnetic valve is controlled to be closed to enable the second branch to be disconnected, oil ejected by the first ejector directly entersthe oil tank and cannot be taken away by airflow at an air suction port of the compressor, and the oil shortage phenomenon of the oil tank is avoided.