Under economic globalization,the expansion and contraction of world’ food supply and demand,and international grain price fluctuations,have a great influence on China to fill its domestic food gap through trade.Therefore,it is very necessary to accurately estimate the long-term global food supply and demand trends.This paper first analyzes the factors that influence the demand for food and grain yield and finds that per capita income,dietary structure,population growth,food prices and the development of bioenergy determine the future trend of the world demand for food.; while grain yield is affected to a great extent by the fertilizer concentration,degree of land development,mechanization degree and the influence of irrigation rate.Based on the estimation of per-capita food demand and grain yields,this paper then adopts trend extrapolation and exponential smoothing model to estimate changing tendency of food supply and demand from 2015 to 2050 in accordance with UN population division’s hypothesis of moderate population growth.The result shows that grain yields growth will be lower in the future,harvested areas will be stablized,wheat and rice demand per capita will be also stablized and corn and soybean demand per capita will remarkably be increasing.In summary,the global food supply will be basically equal to demand,but structural imbalance still exists and there will be rice and soybean gap.