Abstract: An underactuated robot hand with three fingers and ten DOFs has been developed for versatile grasp. It is mainly composed of four mechanisms and driven only by two motors. The design of three phalanges underactuated finger with shape self-adaptation and passive compliance is the most complex among the four mechanisms. This paper discusses the optimal design of the underactuated finger. In the design, we first focus on the static analysis of the underactuated finger and seek for the solution of three normal press forces. Then a reasonable design goal and constraint conditions are proposed, genetic algorithm is employed to optimize the grasp configuration and sizes of the linkages to meet the design goal of the uniform force distribution, compact size, and efficient power transmission.