In this paper,a double direction forecasting technique for monthly rainfall is presented by means of the iterative algorithm based on Chebyshev Polynomials. The double sirection consists of both inter - monthly rainfall and interannual rainfall. The optimum values of the prediction method are a forecast ensemble based on the two-direction prediction values. Choice of the parameters and their forecasting effects are discussed for Chebyshev Polynomial forecasts. Particularly,in order to select ideal initial values a detailed list is made, and by numerical tests the double direction forecasting technique based on Chebyshev Polynomials proves to have higher precision than the single direction forecasting technique under certain conditions.