So far, the detailed design method of the pile-to-pile cap connection by shear keys has not been provided in various design codes, and the design theory of the shear key connection has not been fully developed. Based on the existing research progress, this paper describes several important failure modes, and discusses potential design methods for the shear key connection of steel tubular piles. The findings of this paper may significantly support the development of design methods for the shear-key pile-to-pile cap connections.