Abstract: As an important component of urban wetland vegetation, emergent plants can absorb carbon dioxide and release oxygen through photosynthesis, they can also regulate humidity through transpiration. Thus, they play an important role in improving the well-being of urban residents in high-altitude and arid areas. By measuring the physiological indexes and environmental parameters of reed (Phragmites australis) and cattails (Typha orientalis) in different places and different time periods, the characteristics and influencing factors of their spatiotemporal changes were analyzed. The results showed that: 1) In terms of time, the daily variation of net photosynthetic rate was multi-peak, and that of catcata (14.72 µmol m⁻² s⁻¹) was higher than that of reed (8.46 µmol m⁻² s⁻¹). The transpiration rate of bulrush (7.68 mmol m⁻² s⁻¹) was higher than that of bulrush (3.90 mmol m⁻² s⁻¹). The diurnal variation of water use efficiency was unimodal, and reed (2.34 μmol/mmol) was higher than cattails (2.03 μmol/mmol). 2) In terms of space, the net photosynthetic rate of reed and cattails was higher at the inlet than at the outlet. The transpiration rate of reed inlet was higher than that of outlet, and that of cattails outlet was higher than that of inlet. The water use efficiency of reed inlet was lower than that of outlet, and there was no significant spatial difference in water use efficiency of cattails. 3) Photosynthetically active radiation, water vapor pressure difference, atmospheric temperature and water quality are important factors affecting the spatio-temporal changes of photosynthesis and transpiration of emergent plants. 4) The carbon fixation and oxygen release capacity and humidifying ability of cattail are higher than those of reed. The research results provide a scientific basis for evaluating and improving the ecosystem services of wetlands in Xining City.