Abstract: Abstract: A high-dimensional copula function was introduced to construct the joint distribution of meteorological factors that affected by reference evapotranspiration (ET0). Specifically, an attempt was made to reveal the correlation structure between different variables in copula function, thereby to establish the joint distribution model of multiple meteorological factors on daily ET0 prediction, and finally to analyze short-term drought level. Daily observation data were collected from Dali meteorological station in Erhai watershed from 1954 to 2018. FAO Penman Monteith equation was used to calculate the standard ET0 value for the assessment of forecast precision. T-Tmax two-dimensional normal copula function model was used to predict daily ET0 after screening a variety of meteorological factor datasets. The systematic error appeared between January to April was necessary to be corrected, otherwise it can make the predicted value relatively smaller than the standard ET0. The empirical correction function with error curve was used for the daily ET0 forecast model, to improve the prediction accuracy, thereby to realize the real-time prediction in irrigated region. The results show that: 1) When combining two meteorological factors of T-Tmax, the two-dimensional normal copula model can achieve the highest prediction accuracy for daily ET0, 71.6%, 84.4%, 91.4% and 96.5%, under the relative errors less than 10%, 15%, 20% and 25%, respectively. The annual compliance index IA range was 0.98- 0.99, the average deviation, ME, was 0.17-0.30, the root of mean square error, RMSE, was 0.54-0.64, and the Nash Sutcliffe efficiency coefficient was 0.90-0.98. 2) The daily ET0 prediction method was applied to the prediction and evaluation of daily meteorological drought, taking the daily SPEI index as an example. The correlation coefficient between the prediction value of daily SPEI index and the actual value was 0.95- 0.99, ME was -0.10-0.35, RMSE was 0.20-0.30, IA was 0.97-0.98, NSE was 0.91-0.97, respectively. In the season with more precipitation, the accuracy of Copula function model was higher, and the error parameters of daily SPEI prediction were better, than that of daily ET0 prediction. 3) From the extremely wet year to the extremely dry year, the proportion of humid and light drought days decreased from 81.3% to 46.0%, the proportion of medium drought days increased from 10.7% to 27.9%, and the proportion of heavy drought and extreme drought days increased from 8.2% to 26.2%. In the five typical years of annual precipitation frequency, P= 5%, 25%, 50%, 75% and 95%, the relative deviation of heavy and extremely drought frequency was 1.5% between the predicted ET0 and actual ET0, while reached 1.2% after corrected daily ET0 prediction and actual ET0, to evaluate the daily meteorological drought level. 4) The results also revealed that the frequency of non-drought and light drought was 36.51%, the frequency of moderate drought was 30.37%, the frequency of severe drought and extreme drought was 33.11%, and the prediction deviation was 1.1% from January to June, whereas from July to December, the frequency of humid and light drought was 89.73%, the frequency of moderate drought was 9.07%, the frequency of severe drought and extreme drought was 1.2%, the prediction deviation was 1%, indicating the significant characteristics of seasonal drought.