Abstract: In view of the unclear mechanism evolution of the two-leg shield during the active support process, the planar kinematic model of two-leg shield is established, the necessary conditions for the mechanism evolution of the shield are obtained, and the active cooperative control strategy of the stabilizing ram and the leg is proposed. Theoretical analysis and experimental studies show that whether mechanism evolution occurs in the active support process of the two-leg shield depends on the state of the canopy in contact with the roof and the state of the stabilizing ram; The canopy is in contact with the roof in an elevation, the canopy evolves from a rocker to a "rocker + slider", and the base evolves from a rack to a rocker when the stabilizing ram is a rigid body; When the stabilizing ram is a rigid body, with the leg elongation, the motion form of the canopy is the slide along the roof toward the coal wall and the rotation toward the roof, and the motion form of the base is the rotation around the front toe of the base toward the coal wall, and the motion trajectories of the canopy and the base show a quadratic function, and the larger the elevation angle of the canopy, the greater the distance of the slip of the canopy and the height of the lift of the base; When the stabilizing ram is a floating body, with the leg elongation, the motion form of the canopy is the slide along the roof and the rotation toward the roof, the base does not move, the length of the stabilizing ram changes as a quadratic function, while the trajectory of the canopy shows a cubic function, and the slip distance is very small, as well as reciprocating motion may occur. The proposed active cooperative control strategy of stabilizing ram and the leg can effectively avoid the suction air of stabilizing ram and the mechanism evolution of the shield. The research results reasonably explain the interference phenomenon between shearer and canopy of the shield in Pingdingshan mining area, which provides a new idea for studying the active cooperative control of leg and stabilizing ram.