Abstract: Based on the analysis of forces and deformations of drillstring with large deflection and intermittent contacts with the well wall,the model of the dynamic frictional contact is improved. Solving the double-nonlinear dynamic problem of drillstring by combinning Wilson-θ method with Newton-Raphson method is developed. The computations show it is possible that various kinds of contact exist togather or alternatively, and that dynamic analysis must be done in higher revolution speed.