The utility model relates to a self -lubricating spherical pig includes a seal structure and the 2nd seal structure through setting up, and the 2nd seal structure's front end sets up big piston cylinder, the rear end of big piston cylinder sets up big piston, the middle part front end of big piston cylinder is stuck out forward and is set up the valve piston, thereby utilizes self -lubricating spherical pig puts into the pipeline and carries out the pigging and when removing, move along behind the second leather cup pressurized to compression spring promotes the valve piston and opens the second check valve, closes first check valve, thereby it forms the lubrication to make the interior emollient of big piston cylinder get into through the oil duct between first leather cup and the pipeline wall, carrying on continuously to pour into emollient into during the pigging calibrates the working process between pipeline and spherical pig to prevent effectively that the spherical pig from producing crookedly or even card ball phenomenon, guarantee that it has good sealing performance all the time, ensure the high -efficient completion of the pigging work of calibrating.