There are more and more complex tools and machinery that need be operated by human fingers in our modem industrial environment. Such as computer keyboards, screwdriver, handle wrench, button and switch. All of those should be designed to work effectively and safely with the operators for whom they were designed. At first, ergonomic consideration in design is reachable; this means the operators fingertip must be able to reach the operating component. This is generally no question because human arm has much more degrees of freedom required to position his arms, hands and fingers in the three-dimension space. However, some times we need the finger operate with a fixed wrist. For example in the case in the typing, the reachable workspace of the finger must take into account in such situation.Finger contacting is the most familiar operation mode of the man-machine system, and the index finger takes on the primary operation tasks. From viewpoint of ergonomic engineering, the operation component should be placed within the workspace of the fingertip to reduced or eliminate the movement of palm and arm should to the greatest extent during finger manipulation. Therefore the research of the workspace of ginger is significant to the ergonomic design of the operation device. In this paper, the reachable workspace and workspace under direction restrain 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.