The　article　applied　the　method　of　two-step　back　analysis,　the　value　of　E　(Young＇s　modulus),　P　(horizontal　ground　stress)　and　η(viscous　parameter)　can　be　obtained,　which　can　be　used　to　reflect　the　synthetical　character　of　rock　mass.　Finally　the　rationality　of　inversion　parameters　could　be　verified　and　the　security　of　rock　mass　and　support　structure　could　be　valuated.　To　sum　up,　the　method　of　the　article　could　make　timely　and　accurate　estimation　on　the　stability　of　large　underground　cavern　during　construction,　and　was　very　applicable.