By the analysis on the difficulties for DTH Hammer drilling with casing in soft stratum, the design ideas of combining the impact extrusion drilling and drilling with casing were proposed to complete the structure design of impact extrusion drilling tool with casing. By the finite element analysis software, the simulation analysis on the drilling conditions was made; the calculation results can be instructive to the design and optimization of drilling tools and can be the theoretical basis for the rationality of design of DTH hammer drilling tool structure.