Abstract: A directional well in East China Sea has encountered many obstacles and backing pressure phenomena in the drilling process of 3-opening 12-1/4″ hole. In order to analyze the reasons, this paper is based on a finite element method to establish the static and dynamic calculation models of directional well drill string, to calculate the quasi-static force of drill string during tripping and the dynamic force of drill string during rotary drilling, and to systematically analyze the phenomenon of drill string blockage and backing pressure. The results show that in the wellbore with large inclination, the average contact force between BHA and borehole wall increases, leading to the increase of friction and thus backing pressure phenomenon. The violent collision between the BHA and the wellbore caused the blockage because segments fall off the wellbore. In this paper, reasonable suggestions are put forward to prevent backing pressure in the drilling process of directional well with high inclination, which provides effective reference for safe drilling of directional well in East China Sea.