The utility model relates to a main body mechanism of a four-cylinder spherical explosive motor, which comprises a spherical casing, wherein two ends of the casing are equipped with bearing seats, an intermediate division ring is arranged in the casing, an angle of 35-55 degrees is formed by the intermediate division ring and a connecting line of center through holes of the bearing seats of the two ends of the casing, a gas inlet and outlet opening is disposed on an upper portion or a lower portion corresponding to two sides of an intermediate division rotating plate, the middle portion in the intermediate division rotating plate is equipped with a near-spherical rotating piston, two end portions of the shaft axis of the rotating piston body are hinged with the intermediate division rotating plate, two sides of the rotating piston are correspondingly connected with a piston segment to enable gas cavities located at two sides of the division rotating plate to form four working gas chambers, an internal circular rotating plate is disposed in a slit at the middle portion of the rotating piston, two ends of the internal circular rotating plate are fixedly connected with a main shaft neck which penetrates through holes of the bearings seats of the casing, two gas passages are symmetrically disposed on the internal circular rotating plate, the piston segment is equipped with four gas passage through holes corresponding to the four working gas chambers, and the spherical casing is equipped with a spark plug which extends into the casing. The main body mechanism not only can be used to manufacture an explosive motor with a new working type, but also is compact in structure and few in parts.