The structures of fertilizer tube and fertilizer falling tube have an important impact on the granular multi fertilizer flows blending and fertilizing hysteresis performance in the nutrient proportion of variable rate technology (NPVRT). On the basis of the optimal structure of the blending cavity structure, the granular multi fertilizer variable rate fertilizing process was simulated by discrete element method in this paper, and the impact on particles motion under varied height of fertilizing tube and varied diameter of triangular shape of the bellows was analyzed. According to the proposed performance evaluation indexes, the structures of fertilizing tube and bellows were optimized. The computing and mechanism analysis results show that: first, the greater height of fertilizer tube was, the higher particles speed in falling, collision , mixing and the various stages were. Second, the greater the spread area after the particles colliding with the blending cavity was, the better the particles blending was, and the smaller the standard deviation of particle blending ratio was. Then, the height of triangular shape of the bellows for fertilizer dropping was in range of 4~6mm, relative to the non-bellows one, that could raise the number of collisions among the particles and bellows, thus improving the uniformity of particles blending. However, excessive height slowed down the dropping particles contacted with bellows. If the height of triangular shape of the bellows was about 2mm, that was approximately 40% to 60% the diameter of fertilizer particle, the uniformity blending of particles could be promoted, and triangular shape had smaller effect on time-lagging of particles.