Selecting appropriate inputs for intelligent models is important due to reduce costs and save time and increase accuracy and efficiency of models. The purpose of this study is using Shannon entropy to select the optimum combination of input variables in time series modeling. Monthly time series of precipitation, temperature and radiation in the period of -was used from Tabriz synoptic station. Precipitation, temperature and radiation parameters with different delays are considered as input to the Shannon entropy. The results showed that time series with three delays provide the better results for the modeling. Applying Bayesian network and multivariate linear regression analysis were performed. Models performance was evaluated using three criteria: coefficient of determination (R ), root mean square error (RMSE), and the dispersion. Index (SI). The results indicated that Bayesian neural network model shows the best performance to simulate time series of precipitation, temperature and radiation in compare to multivariate linear regression analysis. The results showed that Shannon entropy has better performance in selection of the appropriate entry into intelligent models.