To achieve the decoupling between the lifting movement and the horizontal movement of a forging manipulator, a kind of manipulator mechanism to achieve the decoupling was presented based on the structural composition principle, and the motion mechanism and the dynamic performance were studied and verified by experiments. Firstly, the composition principle of a fully decoupled forging manipulator was introduced based on the Hoekens four-bar mechanism. The degree of freedom of the fully decoupled forging manipulator was analyzed by using the screw theory, and the decoupling mechanism between the lifting movement and horizontal movement was also dissected. Then the dynamic model was established by using the principle of virtual work. The mechanical behavior between the new mechanism of forging manipulator and the typical parallel-link one was compared and analyzed in the lifting movement and the forging process. Finally, an experimental model of the new forging manipulator mechanism with ratio 1/20 was developed to verify its decoupling performance. Experimental results indicate that during the lifting movement, the displacement variation of the gripper carrier in the horizontal direction remains within 1 mm, which basically verifies that the fully decoupled forging manipulator mechanism achieves the decoupling between the lifting movement and the horizontal movement.