Oncemelania is the middle-parasitifer of schistosome. Controlling the oncomelania is the important way of preventing the schistosomiasis. The article mainly introduces the measurement of jet flow field’s velocity in pressure conduit by FVM numerical modeling and using high-tech PIV, and analyses the reason why the Oncemelania could sink to the bottom but not escape from the equipment named Oncemelania-free intake devices.