The present paper builds a model based on Monte Carlo method in the projection of the blending tobacco.This model is made up of two parts: the projecting points of tobacco materials, whose coordinates are calculated by means of the PPF (projection based on principal component and Fisher criterion) projection method for the tobacco near-infrared spectrum; and the point of tobacco blend, which is produced by linear additive to the projecting point coordinates of tobacco materials.In order to analyze the projection points deviation from initial state levels, Mente Carlo method is introduced to simulate the differences and changes of raw material projection.The results indicate that there are two major factors affecting the relative deviation: the highest proportion of tobacco materials in the blend, which is too high to make the deviation under control; and the quantity of materials, which is so small to control the deviation.The conclusion is close to the principle of actual formulating designing, particularly, the more in the quantity while the lower in proportion of each.Finally the paper figures out the upper limit of the proportions in the different quantity of materials by theory.It also has important reference value for other agricultural products blend.