When tunnel is constructed in karst cave zone, all kinds of filled caverns will be inevitably meet.The construction method and tunnel structure's stability becomes the key problem for the design and construction. The range of DK255+925~+976, filled with crushed rock and silt, forⅠline of Maluqing tunnel on Yichang-Wanzhou Railway is taken as an example. The mechanical responses of excavation and support are studied by using the three-dimensional fast Lagrangian analysis of continua method. The numerical simulation reveals the distribution characteristics of displacement for surrounding rock and displacement and interial stress for the shotcrete and the maximum axis force for locking anchor pipe under the condition of dynamic step excavation and support. The obtained conclusions offer a guideline for the design and construction of tunnels in similar underground projects.