Abstract: The dynamic change pattern of transpiration rate and water use efficiency of Casuarina eguisetfolia in coastline forest were measured using Li6400 portable photosynthesis system. The results showed that the diurnal variation of transpiration rate was single-peak curve, the peak occurred at 12:00 in wet season and 14:00 in dry season, the daily mean in wet season（1.33mmol/(m2·s)）was greater than that in dry season（1.022mmol/(m2·s)），the diurnal variation of transpiration rate was significantly positively correlated with air temperature and photosynthetically active radiation in wet season and significantly positively correlated with air temperature and stomatal conductance in dry season. The seasonal variation of transpiration rate was single-peak curve, which was highest in June and lowest in January，and the average of transpiration rate in different season was summer（1.74mmol/(m2·s)）>spring（1.28mmol/(m2·s)）> autumn（1.24mmol/(m2·s)）>winter（1.06mmol/(m2·s)），the seasonal variation of transpiration rate was significantly positively correlated with air temperature and photosynthetically active radiation and vapor pressure deficit at the leaf. The diurnal variation of water use efficiency was single-peak curve, and the daily change in wet season was greater than that in dry season，the water use efficiency in the morning of dry season was higher than that in wet season, the seasonal variation of water use efficiency was double-peak curve, and the peak occurred at September and January in turn. Therefore, the Casuarina eguisetfolia performed high transpiration rate and water use efficiency under better moisture condition，when the moisture condition was worse, Casuarina eguisetfolia can reduce transpiration rate and improve water use efficiency to maintain its growth, which showed strong adaptability to moisture change.