To make the prosthetic hand move faster with less vibration and smaller than adult thumb,a prosthetic thumb has been designed on the basis of underacutuated mechanism.To make the hand more intelligentized,torque and position perception devices have been integrated.The thumb consists of three joints and is actuated by one motor.And the motor,gearhead and bevel device are all embedded in palm.Planar four-bar linkage and spatial four-bar linkage are adopted between metacarpal and proximal phalanx to make the appearance and track more humanoid.It is verified from experiment that the thumb has faster grasping speed without vibration at the beginning and end of grasping.It is more humanoid when grasping and can accomplish the prehension by subterminal opposition,tridigital grip,cylindrical palmar prehension.and can meet the basic life needs of the handicapped.