Abstract: In order to analyze the internal flow field and features of the low pressure cylinder in the impact process of the high pressure pulse water injection hamm er device, an experiment measuring system and the transient data acquisition system were established to measure and collect the pressure of each measuring point in t he low pressure cylinder under the different trigger spring working and to study the pressure distribution conditions at a same height with different angle within the low p ressure cylinder and the pressure variation conditions at the different height and the water inlet within the low pressure cylinder during the impact process of the water i njection hammer.The experiment showed that the pressure difference at the same height with different angle could be neglected.When the impact was at the zero point, the low pressure zone would be firstly expanded to the middle and top section space of the low pressure cylinder and then steadily expanded to other locations.The pre ssure within the low pressure cylinder and at the water inlet during the impact process would be transiently reduced within a short period and would be kept stable when the final pressure reached.