This paper presents a position and posture control strategy for a n-link planar underactuated manipulator with passive second joint in horizontal plane. The n-link planar underactuated mechanical manipulator is a second-order nonholonomic system, the control objective is to move the end-effector to a given position with a desired posture. The whole control process is divided into n−2 stages. In each stage, the first link is maintained at its initial states unchanged, there exists an angle

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... aint between the passive link and one of the active links. Based on the angle constraints, the target angles of the control objective are calculated by using genetic algorithm. The controllers of each stages are designed, respectively, to achieve the control objective of one of the active links. Finally, taking a 5-link planar underactuated mechanical manipulator, for example, the simulation results demonstrate the validity of the proposed control method.