Grazing and cutting of forages can promote its compensatory growth, which plays an important role in maintaining growth, and resistance to mowing, grazing, trampling. However, little is known about the physiological mechanisms involved in the compensatory growth of grasses. In this study, the growth rate, superoxide dismutase(SOD), peroxide(POD), and catalase(CAT) activities; and soluble sugar, proline, and malondialdehyde(MDA) contents were investigated in the leaves of Lolium perenne L. Light, moderate, severe, and whole cutting levels were used to determine the relationships between antioxidant enzyme activities, osmoregulation and compensatory growth, and the physiological mechanisms of compensatory growth of grasses after cutting. The results showed that the growth rate was higher in the leaves after cutting at the light, moderate, and whole cutting levels, but was lower in the leaves at the severe cutting level than that of control. Compared to that of the control, L. perenne showed significant compensatory growth under light, moderate, and whole cutting levels, and no compensatory growth occurred under severe cutting levels. Normally, in L. perenne, the top of the leaves had higher MDA contents, SOD, and CAT activities, and the base of the leaves had lower MDA, proline contents, SOD, and CAT activities. Compared to the control, at 6 days after different cutting levels, the regrowth of L. perenne leaves had lower MDA, soluble sugar, and proline contents, and lower SOD, and CAT activities. Whereas, at 12 days after different cutting levels, the regrowth of L. perenne leaves still had lower MDA contents, but higher SOD, CAT activities, and proline content. This indicated that cutting decreased the leaf area, reduced the photosynthetic energy availability, and enhanced the compensatory growth function of residual leaves. Therefore, cutting damage was an internal factor resulting in compensatory growth. The compensatory growth rate was correlated positively with the residual leaf size. In addition, although there were differences in the compensatory growth rate in the residual leaves among different cutting levels, the different cutting levels all activated antioxidant enzymes and enhanced proline accumulation. During the compensatory growth of residual leaves, SOD and CAT could scavenge active oxygen free radicals produced during photosynthetic metabolism, inhibit membrane lipid peroxidation, maintain the balance of oxygen free radicals metabolism; and accumulated proline could maintain water balance. Therefore, antioxidant enzymes and osmoregulation play an important role in physiological protection, including photosynthesis and compensatory growth, during rapid self-healing after cutting of residual leaves in L. perenne.