A humanoid manipulator applying to the end effector of an apple picking robot was introduced. Substituting a tendon-actuated manipulator for the simple gripper can improve the adaptability for the end effector to catch apples in intricate surroundings. To realize the open-loop control of the tendon-actuated manipulator, the relationship model of the actuating force and grasping force is necessary. By simulation, the model was established in this paper. Under the same actuating force, the grasping force of the tendonactuated humanoid manipulator was related to the parameters of mechanism. The virtual grasping force was determined by the length and thickness of fingers. The distribution of grasping force was determined by the lengthy proportions of the phalanges. The original angle between the fingers determined the radius range of the apples. As the radius of apples increased, the virtual grasping force decreased. Frictions could homogenize the distribution of grasping force as well as enlarge the virtual force.