Abstract: By using LI-6400 portable photosynthesis system, PAM-2100 chlorophyll fluorescence analyzer, and stable isotope technique, this paper studied the leaf photosynthetic and fluorescence properties, water sources, and water use efficiency (WUE) of five main tree species in coastal shelterbelt forests in Fujian Province, aimed to understand the photosynthetic properties and water use strategies of main tree species in coastal shelterbelt forests in Southeast China. The net photosynthetic rate, intercellular carbon dioxide concentration, stomatal conductance, and transpiration rate of four mangrove species (Kandelia obovata, Aegiceras corniculatum, Avicennia marina, and Sonneratia apetala) were all significantly higher than Australian pine (Casuarina equisetifolia), while the carbon assimilation capacity of the introduced species S. apetala was significantly higher than the native mangrove species. All the measured fluorescence parameters including maximum relative electron transport rate (rETR_max), half-saturation light intensity (E_k), and F_v/F_m of S. apetala were significantly greater than those of native mangroves, indicating that the photosynthetic capacity of S. apetala was also greater than that of the native mangrove species. Two exotic species (C. equisetifolia and S. apetala) mainly relied on groundwater for their water sources, while all indigenous mangrove species could utilize groundwater, rainwater, and seawater. The instantaneous WUE of C. equisetifolia was significantly lower than that of the four mangrove species, while the latter four species had less difference in their instantaneous WUE. The long-term WUE of K. obovata and S. apetala had no significant difference, but was significantly higher than that of A. corniculatum, A. marina, and C. equisetifolia, suggesting that K. obovata and S. apetala could better adapt to the high salt environment where water was the limiting factor for plant growth and survival.