Abstract: With the current data of SODA,geostrophic current data from the satellite altimeter and wind data of ICOADS,we studied on the three-dimensional structural characteristics of the South China Sea western boundary curent and probed particularly into the interannual variability of the western boundary curent along Indo-Chima Peninsula and its relationship with ENS0.The results showed that the core boundary of western boundary current along Indo-China Peninsula could be definedas where themeridional velocity was at 10 cm/s,then its range was from Indo-ChinaPeninsula offshore to 11°E horizontally and shallower than 200m vertically.The variationof the west- ernboundary current volume transport along 12.25°N section showed noticeable positive correlation with ENSO based on 16 a data.Its maximum corelation value reached 0.38 when volume data lagged the ENSO index 5 months with a more than 99%confidence interval.Affecting by the monsoon anomaly during the ENSO,synthesis EI Nino event,from its expansion stage(Jul)to strong stage(Dec),then to decline stage(Julat the following year),the westem boundary curent along Indo-China Peninsula coresponding showed strengthened to weakened,then to weakened mode.However,at the La Nina event,from its expansion stage(Jul)to strong stage(Dec),then to de- cline stage(Julat the following year),thewestern boundary curent varied from weakened to strengthened,then to strengthened in south and weakened in north.In total,ENSO was the main control factor on the interannual varia- bility oftheSouth China Seawestem boundary current.