Based on the NCEP/NCAR reanalysis data of OLR,Nonlinear Principal Component Analysis(NLPCA) are used to research the convective activity over the tropics and its relationship with ENSO.The results show that more nonlinear characteristics of time-space structer are found by using NLPCA than by linear analysis techniques.Such nonlinear characteristics may reflect the nonlinear relationship between tropical convective activities and ENSO.The intensity of OLR anomalies is stronger in the average El Nino period than in the average La Nina period.And the center of OLR anomalies in the averger in the average El Nino period tends to lie at a position east of that in the average La Nina period,thus showing the spatial asymmetry of OLR in the average warm and cold phases of ENSO.