The breech mechanism is a very important part of artillery with a high failure rate. It is planned to build a test-platform for the investigation of the breech mechanism. By this test-platform the motion of the breech, while the artillery is shooting, can be simulated as the same. While the artillery is shooting, the energy for the opening and shutting action of the breechblock comes from the impact between the breechblock operating cam and crank, when the breech is returning. But this action of a hugely heavy thing is very difficult to simulate. So the negative direction action is considered, which makes the breechblock operating cam moved to impact the crank. In this paper the virtual prototype model based on ADAMS is used to measure the load etc. of the key-parts of the breech mechanism by simulation experimentations.