Ginkgo Biloba exocarp may have allelopathy on lettuce, a pot experiment was conducted with 5 grades of exocarp application (0, 15, 30, 60 and 90 g/pot) in order to study of the effects of Ginkgo Biloba exocarp on lettuce growth, antioxidant system, contents of osmotic adjustment substances and photosynthetic system. The results showed that with the increase of lettuce exocarp application, fresh weights of lettuce root length and shoot increased firstly and then decreased, while plant height and stem diameter decreased, and the above lettuce indexes reached the minimum values under 90 g/pot treatment; with the increase of exocarp application, the contents of photosynthetic pigments were decreased significantly compared with the contrast, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity as well as the contents of free proline and soluble protein increased first and then decreased, but malondialdehyde (MDA) content increased insignificantly in lettuce; and with the increase of exocarp application, net photosynthetic rate Pn, intercellular carbon dioxide Ci and transpiration rate of Tr increased first and then decreased, stomatal conductance Gs is dwindling in lettuce. In summary, Ginkgo Biloba exocarp has obvious allelopathic effects on lettuce, inhibiting lettuce growth, physiological characteristics and photosynthetic indexes, the inhibition is strengthened with the increase of exocarp application.