Abstract: A typical event of the sudden decrease in solar wind dynamic pressure (P_Dyn) is observed at 14:24 universal time (UT) on 12 September 2023. The magnitude drops from ~23 nPa to less than 10 nPa within minutes, with a relative decrease larger than 50%. To ensure the reliability of TIEGCM, a data-model comparison is performed. The responses of EIA to the sudden decrease in P_Dyn are estimated in this work, which show an obvious east-west hemispheric asymmetry. EIA is significantly reduced in both the American and African regions. However, in the equatorward of EIA latitudes over Africa, it is weakly enhanced. The primary driver of the EIA responses is the westward prompt penetration electric field (PPEF) during the sudden decrease in P_Dyn. The westward PPEF is simultaneously superposed into the equatorial ionosphere. It drives a downward E×B drift, and suppresses the equatorial fountain effects, hence the generated reduction of EIA. Based on the term analysis in the model, it is found that only vertical E×B drift is responsible for the reduction of EIA during the sudden decrease in P_Dyn. The roles of neutral winds, horizontal E×B drift, and ambipolar diffusion are ignorable. The sudden decrease in P_Dyn is controlled by both the density and velocity of the solar wind. The former and the latter account 114.14% and 41.08% in percentage for the EIA responses, respectively. The non-linear coupling processes account −55.22%.