In this paper, interval fuzzy series forecasting based on GM (1, 1) model is studied. The grey differential equation of GM (1, 1) is improved to suite the interval fuzzy number. The development coefficient is taken as the weighted mean of the development coefficients of the left and right boundary points of the interval fuzzy number. It can indicate the integral development tendency of the interval fuzzy number series. The grey input is taken as the same type of fuzzy number as the raw fuzzy series. Then the binary and ternary interval fuzzy series forecasting are proposed respectively. The examples show the effectiveness of the proposed model.