The invention relates to a using method for a sealer of a well mouth of an oil field. The technical scheme comprises a connecting coupling, an eccentric pressing plate, a packing cavity body, a packing cavity, a sealing packing, a screwing-in inversed tooth, a rotary guiding body and an upper portion compression bolt. The connecting coupling and the eccentric pressing plate are connected through a bolt, the packing cavity body is pressed on the upper portion of the connecting coupling by the eccentric pressing plate, and the packing cavity is formed in the packing cavity body. The packing cavity is connected with the rotary guiding body through a groove in the upper portion of the packing cavity to enable the rotary guiding body to freely rotate. The upper portion compression bolt is connected with the rotary guiding body through a thread. The screwing-in inversed tooth is connected with the rotary guiding body through a protrusion and can move up and down. A polish rod is arranged in the packing cavity and freely moves up and down, and the sealing packing is wound on the polish rod through the screwing-in inversed tooth. The using method for the sealer of the well mouth of the oil field has the beneficial effects that when the sealing packing is replaced, well stopping operation is not required, operating is easy, safety and environment-friendly risks are avoided, the time rate of an oil well is increased, a failed well caused due to the fact that the sealing packing is additionally arranged is avoided, and the using method has significant economic benefits.