In view of the problem that it is hard to achieve independent force and stiffness control for flexible bionic joints, a new equivalent spring model of pneumatic artificial muscle and a joint force and stiffness model are built, and a two-input two-output sliding model controller is constructed to achieve independent force and stiffness control for antagonistic joint driven by pneumatic artificial muscles. Finally, an experimental platform of the pneumatic artificial muscle-driven antagonistic joint is set up. Experiments are conducted to verify the effectiveness of the proposed method under both fixed and open joint position conditions. A comparative experiment is conducted under different loads to verify the universality of the proposed method. The proposed modeling and control scheme comprehensively considers the relatively independent control among position, force and stiffness of the bionic joint, and has a great application prospect in the scenes where a robot interacts with human or environment.