The spatial distribution of wetland vegetation is influenced by a number of hydrological factors, such as groundwater level and soil water content. In order to reveal the characteristics of groundwater level and soil moisture in different vegetation communities, a typical islet wetland of 1.2 km long in Wucheng National Wetland Reserve was selected as our experiment area. In-situ monitoring system was established to collect data of meteorology, soil and hydrology data of the wetland. Observation data showed that groundwater level was in a significant seasonal variation. The largest groundwater depth was up to 10 m in January, while the smallest groundwater depth reached the ground surface in August. It was found that the groundwater level was closely correlated with the lake water level, which implied that the islet wetland aquifer could be in a good hydraulic connection with the lake. The groundwater depth was significantly different along the vegetation gradient, with the mean groundwater depths of 4.76, 2.87 and 1.61 m for Artemisia selengensis, Phragmites and Carex cinerascens communities, respectively. In addition, the numbers of days that the groundwater depth remained for less than 50 cm was 170 d for Carex cinerascens, 112 d for Phragmites and 27 d for Artemisia selengensis, respectively. The soil water content ranged from 2.5%-55.2%, 22.1%-48.1%, and 28.4%-54.1% for Artemisia selengensis, Phragmites and Carex cinerascens communities, respectively. The seasonal variation of soil moisture for Artemisia selengensis demonstrated a higher value in summer and lower ones in other seasons. While the soil content variation for Phragmites and Carex cinerascens communities was similar, with higher water content in spring, summer, and autumn, and lower in winter.