In order to improve the operation capacity of an underactuated prosthetic hand,the static grasp model and the force based impedance control strategy of the finger were constructed based on the underactuated mechanism.According to the static grasp model,the precise relationship between the actuation torque and the support force from phalanges can be obtained corresponding to any grasp attitude.The force based impedance control strategy realizes the force control of base joint.According to experiments,the finger can stably grasp a slippery,fragile,complicated and comparatively heavy object such as an egg.Its success ratio reaches 80%,which can not be achieved only through the force control of base joint(the success rate was only less than 20%).Therefore,the hand can realize complex operation with the construted static grasp model and the force based impedance control strategy.