In order to study the water column separation phenomenon and analyze the factors of pressure boosts and breaking length during the process of stopping a pump for a system, a test model was designed to cause cavity water hammer to occur in two places at the same time. Through the test model, we observed the water column separation phenomena. These phenomena included a completely vaporized state, a completely blocked cavity state, a blocked cavity and vaporized state, and notcompletely block cavity state. The test results show that the initial flow rate and valve closing speed are the two most important factors that influence the water hammer pressure and breaking length. When the flow rate is higher, the water hammer pressure is greater and the breaking length is longer. When the valve closing speed is faster, the water hammer pressure is greater and the breaking length is longer. When there is a higher flow rate, the pipeline layout form has a large influence on water hammer pressure when the pipeline system has devascularization in two places.