There are still uncertainties for permanent E1 Nifio existing in Middle Pliocene. Based on the Pliocene Model Intercomparison Project, the scientific topic of whether or not permanent E1 Nifio exists in the mid-Pliocene is investigated using the Community Climate System Model version 4 (CCSM4), a coupled ocean-atmosphere general circulation model. Model results show that the sea surface temperature (SST)warming is stronger in the eastern equatorial Pacific than that in the western equatorial Pacific,resulting in a reduced west to east SST gradient in the equatorial Pacific during the mid-Pliocene. Because of limited reduced SST gradient, the pattern with high SST in the western equatorial Pacific and low SST in the eastern equatorial Pacific does not change. Moreover,the regional change of other climate variables is also closely related with the changed west to east SST gradient in equatorial Pacific. Besides, the equatorial Pacific SSTs are also characterized by an E1 Nino-Southern Oscillation(ENSO) mode in the mid-Pliocene simulation and the ENSO in the mid-Pliocene is not weaker relative to the pre-industrial. In both mid-Pliocene and pre-industrial simulations, the period of ENSO is also similar to each other. In summary, model results show that permanent E1 Nino conditions do not exist in the mid-Pliocene.