Forest decline in semiarid regions presents a serious ecological threat worldwide. However, the physiological mechanisms of forest trees for surviving in drought conditions are poorly understood. In recent years, the carbon starvation hypothesis has become a research hotspot in physiological processes of trees in drought conditions. Stored non-structural carbohydrates (NSC) could play an important role in tree survival in the face of drought conditions. It has been observed that the NSC concentration of treesvaries under drought conditions. Some studies have suggested that trees close their stomata to prevent hydraulic failure under drought conditions, causing the photosynthetic carbon uptake to decrease, which results in a negative carbon balance, while other studies have shown that trees can maintain the carbon balance and improve NSC storage under drought conditions using certain ecological strategies such as reducing their growth. High calcium is a key characteristic of the calcic horizon, which is widely distributed and considered an important factor affecting tree growth in semiarid areas. Meanwhile, calcium is a key signal substance regulating stomatal closure. Research on the combined effect of high calcium content and drought on carbon balance in trees should deepen the understanding of physiological mechanisms of trees inhabiting semiarid regions. In this study, we proposed two hypotheses: (1) The combined effects of drought and high calcium (drought-high calcium) would significantly reduce the NSC concentration compared with drought conditions alone; (2) These combined effects could alter the distribution of the NSC in different plant tissues and exacerbate the effect of negative carbon balance on trees. To test our hypotheses, we took Quercus acutissima which was not only one of the dominant species of natural forests but also an important afforestation species as experiment material. Then we investigated biomass, photosynthetic characteristics, and NSC concentration in different tissues under drought and drought-high calcium conditions. The results showed that drought stress significantly reduced the biomass of Q. acutissima when compared with the control group not subjected to drought stress, while drought-high calcium stress further reduced Q. acutissima biomass and this decrease was significant when compared with that under drought conditions. Drought-high calcium conditions could significantly decrease the net photosynthetic rate of Q. acutissima seedlings at the early stage of treatment. Photosynthetic rate of Q. acutissima seedlings under drought and drought-high calcium conditions were significantly lower than that of control seedlings after three months, and no difference was observed between the effects of drought and drought-high calcium conditions on photosynthetic rates of seedlings. Drought conditions significantly increased NSC concentration in all tissues of Q. acutissima seedlings, while drought-high calcium conditions significantly reduced the average NSC concentration. Drought and drought-high calcium conditions had different effects on the allocation of NSC to different tissues of Q. acutissima seedlings. Stem was the main tissue for Q. acutissima seedlings to store the increasing NSC under drought conditions in which stem NSC concentration was 52.34% higher than that of control seedlings, and the increase in starch concentration (61.94%) was higher than the increase in soluble sugar concentration (25.53%). Under the combined effects of drought and high calcium content, NSC concentration increased by 32.31% in leaves, but decreased by 49.38% in roots and by 35.31% in stems of Q. acutissima seedlings. We conclude that the combined drought and high calcium conditions decreased NSC concentration in trees as well as their allocation to the stem and root.