According to the related influence factors of grain drying process, the similarity rule for grain drying process was deduced by using dimension analysis. The function expression of the similarity rule and the similarity empirical formula for grain drying process were established according to the experiment. The accuracy of this empirical formula was validated by the experiment. The maximum opposite error between predicting value of empirical model and measurement value of experiment is 2.8%, and the minimum opposite error is 0.7%. The results of experimental validation showed that the empirical model can accurately predict the moisture content of grain at a certain parameters scope.