Abstract: The new technique on depression model test under unsteady flow for lock valves is clarified in this paper, which includes purpose of raising the technique, necessary technical equipment and instruments for unsteady flow tests, characteristics on this technique,comparison on the results by traditional step modeling and unsteady flow modelling under partial vacuity. Due to the obvious difference between steady and unsteady depression model test, new test technique must be used in high lift lock valve cavitation research.