This study focuses on the spatial and temporal distribution characteristics of mesoscale eddies in the South China Sea(SCS). An automatic eddy detection method,based on the geometry of velocity vectors,was adopted to obtain an eddy dataset from 21 years of satellite altimeter data. Analysis revealed that the number of anticyclonic eddies was nearly equal to cyclonic eddies; in the SCS,cyclonic eddies are generally stronger than anticyclonic eddies and anticyclonic eddies are larger and longer-lived than cyclonic eddies. Anticyclonic eddies tend to survive longer in the spring and summer,while cyclonic eddies have longer lifetimes in the autumn and winter. The characteristics and seasonal variations of eddies in the SCS are strongly related to variations in general ocean circulation,in the homogeneity of surface wind stress,and in the unevenness of bottom topography in the SCS. The spatial and temporal variation of mesoscale eddies in the SCS could,therefore,be an important index for understanding local hydrodynamics and regional climate change. This study focuses on the spatial and temporal distribution characteristics of mesoscale eddies in the South China Sea (SCS). An automatic eddy detection method, based on the geometry of velocity vectors, was obtained to obtain an eddy dataset from 21 years of satellite altimeter data . Analysis revealed that the number of anticyclonic eddies was nearly equal to cyclonic eddies; in the SCS, cyclonic eddies are generally stronger than anticyclonic eddies and anticyclonic eddies are larger and longer-lived than cyclonic eddies. Anticyclonic eddies tend to survive longer in the spring and summer, while cyclonic eddies have longer lifetimes in the autumn and winter. The characteristics and seasonal variations of eddies in the SCS are strongly related to variations in general ocean circulation, in the homogeneity of surface wind stress, and in the unevenness of bottom topography in the SCS. The spatial and temporal variation of mesoscale eddies in the SCS could, therefore, be an important index for un derstanding local hydrodynamics and regional climate change.