Abstract: In order to explore canopy photosynthesis of desert plant Calligonum potanini, and characteristics of carbon source and carbon sink in arid desert area, the canopy apparent photosynthesis and soil CO2 efflux rate were measured in high temperature and irradiation and suitable environment periods by the modified assimilation chamber and LI-8100 automated soil CO2 flux system in two years. The results showed that the difference of canopy apparent photosynthetic rate (CAP) of C. potanini in different years and months was significant, the canopy photosynthesis was enhanced significantly with improving soil water, the.average CAP (08:00.18:00) was 1.82 mol/ (m2·s) in high temperature and irradiation period and 2.89 mol/ (m2·s) in suitable environment period, respectively. The calculated formula of CAP by photosynthetic rate of assimilating shoots (Pn) was CAP = 0.12Pn + 0.39 (r = 0.86, P 0.000 1) in high temperature and irradiation period and CAP =0.18Pn +0.28 (r =0.92, P 0.000 1) in suitable environment period. The soil CO2 efflux rate under plant canopy was 0.29 μmol/ (m2·s) in growth period, and it was 0.15 μmol/ (m2·s) in desert bare land. The fixed carbon of C. potanini canopy in growth period was 3.82 g/ (m2·a), the released carbon under plant canopy was 1.03 and 0.53 g/ (m2· a) in desert bare land in the same period. These results indicated that the increasing in canopy apparent photosynthetic rate of desert plant C. potanini exceeded the increasing range of soil water in the layers of root mainly distributed in the water shortage desert area; it doubled in suitable environment period. The soil respiration rate of desert ecosystem was lower and that in desert bare land was about 50% of that under plant canopy. The zone of desert plant C. potanini population was a weak carbon source.