Abstract: As one of the most important types of renewable and clean energies, solar energy resources are substantially influenced by climate factors. Based on the monthly sea surface temperature dataset from the Hadley Center and the atmospheric reanalysis dataset from the fifth generation of the European Centre for Medium-range Weather Forecasts reanalysis for the 1979–2023 period, this paper investigates the possible effects of El Niño–Southern Oscillation (ENSO) on the total solar irradiation (TSI) during different seasons in central-eastern China using the correlation analysis, regression analysis, and composite analysis. TSI in central-eastern China is found to exhibit pronounced interannual variability, which is closely related to ENSO. During the developing summer and autumn of an El Niño event, the TSI anomaly exhibits a dipole structure of “positive in the north and negative in the south”. This pattern shifts to a monotonic pattern in central-eastern China during the mature winter season, with the peak anomaly located in southern China. During the El Niño decaying spring, a dipole structure of “positive in the southwest and negative in the east” is observed. In addition, during the El Niño decaying summer, the negative TSI anomaly is detected in the region of the upper and middle reaches of the Yangtze River. When La Niña events occur, the anomaly patterns are generally reversed but with a smaller amplitude, indicating an asymmetric ENSO influence on TSI to some extent. Further analysis reveals that the ENSO influence is related to the reflection effect by the total cloud cover change resulting from the ENSO-induced atmospheric anomalies in circulation and humidity. The results of this paper indicate important implications for the seasonal-to-interannual prediction of photovoltaic power capacity and for the related benefit assessment.