Abstract: This research used Penicillium digitatum as test microorganism to study the effects of different doses of gamma irradiation (0.25, 0.50, 0.75 and 1.00 kGy) on the growth, the relative electric conductivity of culture solution, total sugar and soluble protein contents of the mycelium, activity of malate dehydrogenase and succinate dehydrogenase. In addition, effects of different doses of gamma irradiation on the weight loss rate, respiration intensity, the contents of soluble solids, organic acids and ascorbic acid of Ponkan fruit were studied. The results showed that, the normal growth of Penicillium digitatum was inhibited by gamma irradiation and the inhibitory ratio increased with the gamma irradiation doses arised. Meanwhile, gamma irradiation could enhance the cytomembrane permeability of mycelium, reduce the total sugar and soluble proteins contents in the mycelium and metabolism, thereby disrupting the normal physiological metabolism of Penicillium digitatum. Furthermore, different dose of gamma irradiation could influence the postharvest physiology of Ponkan fruit at different levels. Compared with others, 0.5 kGy gamma irradiation reduced the weight loss rate, respiration intensity, inhibite the degradation of soluble solids, organic acids and ascorbic acid of the Ponkan fruit had the best effects.