Abstract: The soil deformation mechanism is a complicated nonlinear problem in the percussion-extruding drilling process of downhole drills.As of the contact problem of downhole drills to soils,the author in this paper establishes a finite element analysis model that uses downhole drills for percussion-extruding drilling in soil on the basis of adopting the Drucker-Prager yield criterion,taking soil as DP materials,and simulating the drilling process according to the contact and press load of drilling tools to soils.Based on the finite element method of non-linear transient dynamics,the impact force of downhole drills to soils is studied and the stress and strain of soils around the drilling tools and the friction between drilling tools and soils are analyzed.Research results show that there are stress concentration bulbs near the cone bit,and the impact energy is mainly used to compress soils in vertical direction while the compress effect is smaller in horizontal direction.The peak value of the frictional stress is located near the bit cone surface,which is one the main factors affecting drilling speed.