Abstract: In this paper, Bottom Hole Assembly in a curved wellbore is treated as spatial elastic beam. On the basis of geometrically nonlinear strain analysis, tangent stiffness matrixes are deduced. Then the boundary nonlinear problem considering fiction force between drillstring and well wall has been dealt with by the method of "applying" or "deleting" constraints. The basic formulations for the double nonlinear finite element analysis of drillstring in the large curvature wellbore are set up, and the Newton-Raphson iteration method is employed to solve the non- linear equations. Numerical and engineering examples are studied to verify the reliability of the present method. The present work can provide useful reference for the large curvature wellbore trajectory prediction and simulation.