In order to analyze the stochastic impact on grain price,this paper uses Beveridge-Nelson decomposition to decompose stochastic trend and cycle of main grain prices and utilizes Cochrane variance ratio to test the influence of stochastic impact.The result shows that prices of indica,japonica,corn and soybean demonstrate steadily increasing determinant trend and negative stochastic trend and the stochastic impact on the grain prices is extremely negative,especially from 1998 to 2003.The grain prices’ cyclical fluctuation is significant,and it is influenced by the stochastic impact.In the short term,the influence of stochastic impact on price of indica,japonica and soybean reaches the maximum in the 20th period,while the corn price reaches the maximum in the 10th period which is the key factor of the short-term price fluctuation.