Lakeside desertification is a common type of desertification in South China. Soil moisture dynamics of lakeside sandy land have important implications for regional vegetation restoration and reconstruction. Using soil moisture data from the Duobao Sand Hills of Poyang Lake recorded from February 2013 to February 2014, we investigated soil moisture dynamics under different vegetation coverage and extreme weather conditions. We found that (1) soil moisture levels of lakeside sandy land in the rainy season were significantly different from the levels in the drought season. Soil moisture, mainly affected by precipitation, was maintained at a higher level ( > 0.063 cm³/cm³) and was less sensitive to the type of underlying surface in the rainy season. However, different types of vegetation cover affected soil moisture differently. Soil moisture in the presence of Pinus elliottii was relatively low ( < 0.035 cm³/cm³) during the drought period. (2) Under high temperatures and drought conditions, shallow-soil moisture of desertified lands dropped rapidly at first, then remained exceptionally low ( < 0.01 cm³/cm³). With the increase in soil depth, the differences in soil moisture among soils with Pinus elliottii, Vitex trifolia Linn., or bare sandy lands became more significant. (3) 17-year-old Pinus elliottii effectively increased the water-holding capacity of the soil surface during the rainy season. However, due to water absorption and obstruction of rainfall, Pinus elliottii affected groundwater recharge during the drought period in terms of the amount of water and soil depth. Therefore, the shallow-soil water of a 17-year-old Pinus elliottii stand is difficult to recharge when precipitation intensity is low. Based on our findings, we suggest to increasing the initial planting density of Pinus elliottii then decreasing mature Pinus elliottii density in subtropical sandy land in South China to neutralize the effects of more frequent extreme droughts and to induce continuous positive succession in desertified areas.