Abstract: To control the trajectory by means of Bottom Hole Assembly(BHA) design effectively,based on the rock-bit interaction model and the mechanical analysis of BHA,the future trajectory could be calculated by modeling the process of drilling.An optimal method of BHA parameters design for controlling trajectory was established,where the minimum error between the modeling trajectory and the design trajectory was the objective function and the BHA design parameters and operating parameters were decision variables.The practical application shows that the result is accurate and the method can tell whether the design of BHA is proper effectively.