The invention discloses a pendulum cylinder pneumatic engine. The end of a driving shaft is fixedly connected with a crankshaft, and the crankshaft is rotationally connected with the lower end of a movable rod. The upper portion of the movable rod is sleeved with the lower portion of a cylinder. The upper end of the movable rod is fixedly connected with a piston block. The edge of the piston blockis in sliding connection with the inner wall of the cylinder in a sealed manner, and the middle of the cylinder is sleeved with a lantern ring. The middle of the lantern ring is fixedly connected with the end of a connecting shaft. The other end of the connecting shaft is connected with another bearing inner race. A bearing outer race is fixedly connected with another bearing pedestal. The bearing pedestal is fixedly connected with the center of the upper portion of a crankcase. The engine breaks through structural characteristics of traditional internal combustion engines, the cylinder fixedto the crankcase is separated, all cylinders can become components which can oscillate left and right along with corresponding connecting rods, through such changes, the stroke-bore ratio (S/D) of the internal combustion engine is directly increased by several times or even more from 0.8-1.2, thus, the turning radius of the crankshaft can be increased by several times or even more, and the requirement for the large torque of the engine is met.