Abstract: If the flameproof electrical apparatus is composed of two or more chambers, it would be easy to produce pilling pressure phenomenon as gas explosion in chambers. In general, pilling pressure will cause the explosion pressure rise sharply, which means larger explosion pressure than expected, so the pilling pressure should be avoided, or increasing the enclosure strength to meet the explosion resistance performance. In this article, through many experiments, we determine the reference pressure testing point and explosive path of two chambers flame-proof sample, which provides reference pressure test and flame-proof performance design for two connected chambers type flameproof electrical apparatus.