Abstract: The present invention relates to a deaeration device for deaerating water used during ultrasonic focusing tumour treatment. The said deaeration device includes water purifiers (2), a vacuum pump (32), a water heater (6), electromagnetic valves (3, 5, 7-9, 19-23, 25-26, 30-31), water tanks (10, 18), content gauges (11, 15, 17), a thermometer (13), vacuum gauges (12, 16), and an aqueous capsule (24). The said vacuum pump (32) is a water jet vacuum pump, and there are two water tanks (10, 18). The vacuum pump (32) is connected to the tops of two water tanks (10,18) via a valve assembly composed of four electromagnetic valves (19-22). Two atomizing nozzles (14) are respectively provided at the water inlets on the tops of two water tanks (10,18).