Plants depend on resources from the environment for photosynthesis. Climate change may affect the supply of photosynthetic resources, especially water and light. Water use efficiency (WUE=maximum net photosynthetic rate [P_nmax]/stomatal conductance [g_s]) is a key parameter to evaluate how plants balance the trade-off between carbon gain and water loss. Light use efficiency (LUE) is highly related to the production of the whole plant community. Recently, how to accurately predict WUE and LUE, the key ecophysiological parameters, have received widely attention. To better understand the ecological adaption of vegetation to climate change, we measured leaf light response curves of Cotinus coggygria, a widely distributed shrub in mountainous areas in Beijing, using LI-6800 portable photosynthetic analyzer from May to October 2021, i.e., leaf expanded period. This study aims to examined seasonal dynamics of water and light use efficiencies and their regulating factors. Results showed that the WUE decreased from May to June, then staying relatively stable from July to October. The LUE increased from May to July, then staying relatively stable from August to October. The means of WUE and LUE during the study period were 98.25 μmol/mol and 0.06 mol/mol, respectively. The coefficients of variation of WUE and LUE were 22% and 17%, respectively. WUE had a negative correlation with LUE (R²=0.86; P<0.01). WUE and LUE were mainly affected by soil water content (SWC) among environmental factors. Specifically, WUE decreased linearly with increasing SWC, whereas LUE increased linearly with SWC. Furthermore, for every 0.1 m³/m³ increase in SWC, P_nmax, and g_s increased linearly by 4.23 μmol m^-2 s^-1 and 0.07 mol m^-2 s^-1, respectively. The sensitivity of g_s to SWC was higher than that of P_nmax. The effect of photosynthetically active radiation (PAR) on WUE and LUE was weak. For biological factors, WUE and LUE were mainly affected by specific leaf area (SLA). WUE increased with SLA, while LUE decreased with SLA. There was no significant correlation between leaf nitrogen content (LNC) and WUE, LUE. Two-factor linear models combining SWC and SLA performed well in simulating WUE and LUE (R²=91% and 71%, respectively), and the standardized regression coefficient of SWC was greater than SLA. These results suggest that SWC was the main environmental factor limiting WUE and LUE, and SLA was the key biological factor regulating them. Furthermore, SWC played a more important role than SLA in regulating seasonal WUE and LUE. Our findings have important implication for understanding the eco-function changes of shrubs in mountainous areas in Beijing under climate change.