The existing ENSO indices are defined based on the sea surface temperatue anomalies (SSTAs) in different regions of the equatorial Pacific. Considering that the tropical convective activities are closely related with ENSO and the impact of ENSO on the large-scale atmospheric circulation is mainly through the release of latent heat caused by the associated convective anomalies, a new ENSO index, the tropical convection index (ITC), is defined based on the zonal dipole distribution of outgoing long wave radiation anomalies over the equatorial Pacific. The ITC index can well represent ENSO events and their interannual variation. Compared to the existing ENSO indices, the ITC index is more closely related to the East Asian winter monsoon (EAWM) and can better depict the impact of ENSO on the EAWM. The ITC index provides a new index for ENSO monitoring, predicting and impact, eliminating the inconvenience that numerous existing ENSO indices may have caused.