Abstract: A continuous electric driving scheme for quadruped robot leg (that is, the motor rotates cyclically to drive the leg to swing and step) is proposed. A robot leg structure with two-degree-of-freedom double crank composite link mechanism is designed, which is composed of a Chebyshev mechanism and a five-bar mechanism. The trajectory characteristics of animal foot are analyzed, and the elliptic curve with smooth trajectory, no mutation and continuous derivative is used to plan robot foot trajectory. With the implementation of the planned foot trajectory as the optimization objective, the optimum size of leg mechanism is obtained with the genetic algorithm and the interior point method in fmincon function. On this basis, a simulation model of quadruped robot is built, and the motion characteristics of foot are analyzed through Adams simulation. A performance test platform for leg structure is also developed. The experiment of single foot motion trajectory tracking is conducted to verify the feasibility of the proposed robot leg structure.