A runner cycloid speed changing stress application mechanism is composed of a machine body (1), a bent axle (2), a runner (3), a cycloidal wheel (4) and a bent wheel axle (5). The runner (3) is eccentrically installed relative to an axle body (6) of the bent axle (2). A wheel body (15) of the cycloidal wheel (4) is installed in an eccentric bearing roller path (11) of the runner (3) in a bearing support manner. An axle neck (13) of the bent axle (2) is installed in an eccentric bent axle roller bath (12) of the cycloidal wheel (4) in a bearing support manner. The bent axle (2) rotates by a circle at a constant speed, and the bent wheel axle (5) rotates by a circle in a speed changing manner under the effect of revolution and rotation of the cycloidal wheel (4). When the bent axle (2) is in the constant power input condition, according to the fact that the power is equal to the product of force and speed, when the bent wheel axle (5) decelerates, the torsion is increased, and accordingly the constantly-increasing reverse acting force, generated in the compression exhaust stroke, of a piston (19) is overcome.