By analyzing the variability of global SST(sea surface temperature) anomalies,we propose a unified Ni o index using the surface thermal centroid anomaly of the region along the Pacific equator embraced by the 0.7°C contour line of the standard deviation of the SST anomalies and try to unify the traditional Ni o regions into a single entity.The unified Ni o region covers almost all of the traditional Ni o regions.The anomaly time series of the averaged SST over this region are closely correlated to historical Ni o indices.The anomaly time series of the zonal and meridional thermal centroid have close correlation with historical TNI(Trans-Ni o index) indices,showing differences among El Ni o(La Ni a) events.The meridional centroid anomaly suggests that areas of maximum temperature anomaly are moving meridionally(although slightly) with synchronous zonal movement.The zonal centroid anomalies of the unified Ni o region are found helpful in the classification of the Eastern Pacific(EP)/Central Pacific(CP) types of El Ni o events.More importantly,the zonal centroid anomaly shows that warm areas might move during a single warming/cooling phase.All the current Ni o indices can be well represented by a simple linear combination of unified Ni o indices,which suggests that the thermal anomaly(SSTA) and thermal centroid location anomaly of the unified Ni o region would yield a more complete image of each El Ni o/ La Ni a event. By analyzing the variability of global SST (sea surface temperature) anomalies, we propose a unified Ni o index using the surface thermal centroid anomaly of the region along the Pacific equator embraced by the 0.7 ° C contour line of the standard deviation of the SST anomalies and try to unify the traditional Ni o regions into a single entity. unified Ni o region covers almost all of the traditional Ni o regions. The anomaly time series of the averaged SST over this region are both correlated to historical Ni o indices. anomaly time series of the zonal and meridional thermal centroid have close correlation with historical TNI (Trans-Ni o index) indices, showing differences among El Ni o (La Ni a) events. meridional centroid anomaly suggests that areas of maximum temperature anomaly are moving meridionally (although slightly) with synchronous zonal movement. The zonal centroid anomalies of the unified Ni o region are found in the classification of the Eastern Pacific (EP) / Cen tral Pacific (CP) types of El Ni o events. Importantly, the zonal centroid anomaly shows that warm areas might move during a single warming / cooling phase. All current Ni o indices can be well represented by a simple linear combination of unified Ni o indices, which suggests that the thermal anomaly (SSTA) and thermal centroid location anomaly of the unified Ni o region would yield a more complete image of each El Ni o / La Ni a event.