The invention relates to the field of breeding technology, and particularly relates to a fixing device and a method for mouth opening and drug feeding in live pig breeding. The fixing device includesa base and a top plate, the top of the base is symmetrically provided with two support plates, and the fixing device also includes a controller, a pressing mechanism and an enclosing-barring mechanism. The enclosing-barring mechanism includes a vertical plate, an enclosing assembly and two barring plates, and the pressing mechanism comprises a standing board, a cross bar, two traction assemblies,two pulling-down assemblies and two compressing assemblies, the top of the base is symmetrically provided with two guide rods, the outer wall of each guide rod is provided with a sliding column in a sleeved mode, the center of the bottom of the cross bar is fixedly provided with a horizontal plate, and the enclosing assembly and the controller are electrically connected. The fixing device and themethod for mouth opening and drug feeding in live pig breeding can effectively fix the head and other parts of the body of pigs of different sizes, the pig is not easy to struggle, so that it is convenient to carry out drug feeding, and the drug-feeding personnel is not easy to be injured, with low safety risk.