In order to solve the problem that no functional type of prosthetic finger is suitable for handicapped person with only truncated base knuckle,a novel partial finger was designed in this paper.First,the characteristic of truncated base knuckle was analyzed.Based on the passive drive principle,mechanical structure of the partial finger was designed.Then,research on the motion law of the knuckles was carried out based on personification ideas,and parameters of the bars were determined to realize the approximate equal ratio transmission.Finally the kinematics analysis as well as the performance experiment was done.The partial finger with its size smaller than the little finger of an adult is driven by truncated base knuckle and has two degrees of freedom,moreover,each joint approximately moves with stable drive ratio.Experimental results indicate that the disassembly and installation of partial finger can be accomplished only by one hand,the maximum force output by fingertip is 10.7 N,the shape and motion of partial finger are similar as the human finger,and no problem appears after 50 thousand of fatigue tests.The partial finger can accomplish 95 percent of the hand function with the cooperation of other fingers.