Abstract: The photosynthetic characteristics of two main walnut varieties in southern Xinjiang basin were analyzed and compared, in order to provide scientific basis for the cultivation and breeding of Juglans regia in southern Xinjiang Basin. The J. regia "Wen185" and J. regia "Xinxin2" in the southern Xinjiang basin as the research object, the photosynthetic characteristics, photosynthetic parameters and chlorophyll fluorescence parameters of different growth stages of the fruit were measured by LI-6400 and FMS-2, and analysis the photosynthetic characteristics. Results show the LSP of J. regia "Wen185" is maximum in the near mature stage, The LSP of J. regia "Xinxin2" is maximum in the fatty phase, the Pn of two walnut varieties are the highest in the hard core stage; Sunny weather conditions, the curve of diurnal variation of net photosynthesis rate showed two single peak of two walnut varieties fruit at different growth stages, obvious midday depression of photosynthesis, and the phenomenon of "midday depression" was accompanied with the decrease of Ci and the increase of LS; Photo inhibition occurred of two walnut varieties fruit at different growth stages, and the decrease of Fo is accompanied by photo inhibition. In-depth analysis available that the phenomenon of "midday depression of Photosynthesis" of two walnut cultivars is caused by stomata limitation factors and the occurrence of photo inhibition is not caused by the destruction of optical system, but because of the non radiant energy dissipation.