Grasping a moving target has been investigated extensively for fixed-base manipulator. However, such a task becomes much more challenging when the manipulator is free flying in the air with an UAV. Towards moving target grasping, this paper presents an aerial manipulator system composed of a hex-rotor and a 7-DoF (Degree of Freedom) manipulator. An independent control structure is used in the aerial manipulator control system, i.e., the hex-rotor and the manipulator are controlled separately. In the hex-controller, the system CoM (Center of Mass) offset motion is used to compensate disturbance of the robotic arm. the relative kinematics between the target and the aerial vehicle is taken into consideration to grasp the target. At last aerial grasping experiments are conducted to validate the feasibility of the proposed control scheme and the reliability of our aerial manipulator system.