Abstract: In this paper, a modified synthetic decision model is proposed on the basis of a synthetic decision model with general fuzzy operation with an example of crop yield forecast. By adopting the piecewise regression method and stepwise regression method, a quantitative model for crop yield forecast has been established and compared with the mentioned synthetic decision model. The two models are mutually complementary, and they can simulate 88% of historical data very well, but moreover their reliability has been confirmed by the measured values obtained in 1983. In every aspect, by using the synthetic decision model, the results of crop yield forecast are quite satisfactory.