In this paper, the problems are discussed for shape design and position arrangement for Water Strider Robot's supporting legs are discussed. A supporting leg is approached as Euler-Bernoulli elastic curved beam and a method for designing its optimal shape is proposed by analysing elastic deformation and stress-strain. The objective of the proposed optimal method is to attain the maximum lift force in leg operation. The effectiveness and validity of design results are verified through simulations and lab experiments. A method for properly locating supporting legs on the robot body is proposed by analysing the influence of leg location to lift force and the relationship of supporting legs' with robot's roll-resistant capability. A layout scheme for the Water Dancer II-a prototype with ten supporting legs is presented with its operation successful designed.