Stem photosynthesis reassimilates CO₂ that released from their own respiration, which effectively reduces the CO₂ efflux to the atmosphere. In this study, Haloxylon persicum, the dominant woody plant in Gurbantunggut Desert, was selected as the research object. A portable LI-6400 photosynthesis system combined with P-Chamber was used to observe the light response and diurnal photosynthetic characteristics of leaves and stems. The environmental factors, including temperature and humidity, photosynthetically active radiation, soil temperature and water content, and leaf or stem traits (chlorophyll content, water content, dry matter content, carbon or nitrogen content, etc.) were monitored to reveal the main influencing factors of leaf or stem photosynthesis. The destructive sampling was used to quantify the total surface area of leaves and stems to clarify the contribution of stem photosynthesis to individual carbon balance. The results showed that:(1) the chlorophyll content of the leaves was 12-16 times than that of stems in H. persicum, and there was no significant difference in chlorophyll content among different diameter stems. (2) The light saturation point of the stems was lower than that of the leaves, and the dark respiration rate and photosynthesis of different diameter classes (from coarse to fine) of stems gradually decreased. (3) The photosynthetic effective radiation, soil moisture and air temperature and humidity were the main factors affecting leaf photosynthesis, but had no significant effect on stem photosynthesis. There was a strong correlation between stem photosynthesis and stem. (4) Stem photosynthesis fixed 73% of CO₂ produced by its own respiration, and the highest rate reached 90%, photosynthetic CO₂ fixation in stems accounted for about 15.4% of individual level carbon fixation. The results of this study show that there may be a fundamental defect in ignoring the contribution of stem photosynthesis to predict the carbon process of desert ecosystem under the background of future climate change. When estimating the stem respiration, it is necessary to consider whether there is stem photosynthesis to improve the accuracy of branch respiration.