As time cost and energy consumption of ball milling smash of native starch are both high and the product is easy to gelatinize,acid pretreatment before the milling was introduced in the preparation of micronized starch.The corresponding physicochemical properties of the product,including the particle size,the granule morphology and the crystalline structure,were then investigated.The results show that（1） ball milling greatly affects the granule morphology and the crystalline structure but it produces no effect on the particle size of native starch;（2） acid pretreatment makes the milling easy and results in a decrease in particle size of the micronized starch;（3） the content of small particles（in a size of less than 10μm） in the micronized starch with acid pretreatment（the hydrolysis rate being 8.80%） is 72.58%,which is greatly higher than the value 16.76% of the native starch;（4） with the implementing of ball milling,some micronized starches aggregate;and（5） after the acid pretreatment,the crystalline structure of the micronized starch is partially destroyed,part of the Maltese cross disappears,the birefringence intensity weakens,and the degree of crystallization decreases significantly.