Abstract: In order to better utilize light resources in Mengding basin, the author adopted monthly sunshine duration data from the meteorological station in Mengding basin from 1961 to 2008, used the linear trend method, harmonic analysis, Mann Kendall test, R/S analysis and forecast model of average growing function to analyze the changes of sunshine duration and its future trend of Mengding basin in recent 48 years. The study suggested that the annual sunshine duration presented a trend of decrease, the change rate was -94.64 h per decade, decreased 454.3 h in recent 48 years, the largest contribution to the annual sunshine duration decrease was the rainy season, annual and seasonal sunshine duration showed a trend of decrease. Except winter, the annual sunshine duration and that of the other seasons from 1980 to 1999 broke the -2.58 borderline and the winter mutation decreased significantly with the change cycle of 5 years. The significantly decreased evaporation capacity and the increase of relative humidity were the main reasons for the decrease of sunshine duration. Sunshine duration could still show a trend of significant reduction from 2009 to 2023.