Abstract: when the behaviour of main pump in PWR power plant change,as a result of arresting fluid countercurrent current by check valve,water hammer phenomena met occur more or less in loop.Serious water hammer not only met brought incident of over pressure,imperil pressure boundary,but also may en-gender check valve lapse.DC check valve is a kind of new theory check valve,is designed to avoid serious water hammer phenomena at tradition check valve closing.the analyses and experiment indicate that DC check valve can availably solve water hammer problem in the loop,and be able to reliably prevent fluid countercurrent.