[Objective]: This study aims to reveal the interspecific differences and dynamic variations in water use efficiency (WUE) of coniferous tree species in urban environments of semi-arid regions, clarify the regulatory mechanisms of environmental factors on WUE, and provide a scientific basis for selecting water-saving urban greening tree species. [Methods]: The study was conducted in Hohhot. Four common urban greening conifers—Platycladus orientalis, Juniperus rigida, Pinus tabuliformis and Picea meyeri—were selected as experimental materials. A pot-controlled experiment with a completely randomized design was employed. Using a LI-6400XT portable photosynthesis system, photosynthetic parameters including net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO? concentration were systematically measured during the growing season from June to September 2024. Instantaneous water use efficiency was calculated. Environmental factors such as photosynthetically active radiation, temperature, and relative humidity were monitored simultaneously. Statistical analyses were performed using repeated measures ANOVA and Pearson correlation analysis. [Results]: Pairwise multiple comparisons of the four tree species using Tukey's HSD test showed extremely significant differences between all species (P < 0.001). The mean WUE during the growing season followed the order: Juniperus rigida > Platycladus orientalis > Pinus tabuliformis > Picea meyeri. Juniperus rigida had the highest WUE (6.16±0.80 μmol·mmol?1), employing a conservative water use strategy characterized by low photosynthesis and low transpiration. Platycladus orientalis exhibited a moderate WUE (3.64±0.96 μmol·mmol?1). Pinus tabuliformis and Picea meyeri had lower WUE values, at 1.62±0.73 and 0.99±0.67 μmol·mmol?1, respectively. Correlation analysis indicated that WUE was significantly positively correlated with net photosynthetic rate and leaf-to-air vapor pressure deficit, and significantly negatively correlated with stomatal conductance and transpiration rate. [Conclusion]: Juniperus rigida, with its conservative water-use strategy characterized by "low photosynthesis and low transpiration," demonstrated the highest water-use efficiency and exhibited highly efficient and stable performance under the controlled pot experiment conditions in this study. It can be prioritized for urban greening in semi-arid regions with artificial maintenance or similar water management practices. Platycladus orientalis showed a well-balanced water-use strategy and strong adaptability. In contrast, the high water consumption and low stability of Pinus tabuliformis and Picea meyeri spruce make them unsuitable for promotion in water-limited environments. This study provides an important theoretical basis for the scientific selection of urban greening tree species and the construction of water-efficient urban forest ecosystems in semi-arid regions.