Abstract: Muscle fiber was basic unit for constructing muscle and muscle fiber characteristics had direct impacts on pork quality. According to polymorphism of myosin heavy chain （MyHC）, porcine muscle fibers were divided into four types： 1, 2a, 2b and 2x, and they were corresponded to the slow-oxidative type, fast-oxidative type, fast glyeolytic type and the intermediate type by the metabolism. The generation of muscle fiber was regulated exaedy by the myogenin gene on the molecular level. The muscle fiber type converted in the process of growth constantly, and it was influenced by many factors such as heredity, growth, sex, nutrition and others factors.