Two-dimensional transient shock wave focusing experiment system was designed to investigate the shock wave focusing initiation energy of two-stage pulse detonation engine. Dynamic pressure sensors and particle image velocimetry system were adopted to capture the dynamic pressure of the cavity bottom vertex and the velocity vector field during multi-cycle of shock focus. Furthermore

the cavities of type A and B were used in contrast tests and the velocity vector field was analyed in the meantime. It was found that the first focus was caused by incident shock produced by diaphragm rupture. The post-focus reflected wave formed immediately after shock focus reflected at jet boundary of the nozzle exit and generated the re-reflected wave. The re-reflected wave acted a incident shock in the second cycle and contributed to the second shock focus

then periodic shock focus formed. The focus frequency was up to 7-10kHz. In addition

the velocity field and the strength of the jet weakened with the collision of incident shock waves

then enhanced when high-pressure flow was exhausted

forming a cyclical change.