The reachable workspace and workspace under direction restraint of contacting for the index finger are determined using serial mechanism model and the Penalty Function Method based on geometric measurement of human body. The optimal operating position and orientation of human finger is analyzed in accordance with the size and situation of finger workspace. The laying of the press button and pull-push switch is also analyzed. A new ergonomic tilting computer keyboard design is put forward as a case study. The results of this paper may be used to achieve ergonomic design of operation system for the human finger, to relieve fatigue of operator, as well as to improve the efficiencies.