Abstract: To investigate grinding method on micro cracks characteristics in grain of ground products，using a magnetite ore from Eastern Hebei Province area as object，comparison of products from high pressure roller mill and jaw crusher was conducted.Micro cracks characteristics difference was analyzed on different crushing products.Influence of micro cracks on ground products was studied by detection of Bond Ball Mill Work Index.The results show that the number of cracks and cleavage cracks ground by high-pressure roller mill were significantly higher than that of jaw crusher products，with the decrease in particle size range，micro crack length，width and number were increased，while the product particles surface roughness also increased significantly；The Bond Ball Mill Work Index (target particle size -0.15 mm and -0.074 mm) decreased by 13.55% and 14.14% respectively.Using high pressure roller mill can effectively reduce the grinding energy consumption；Under the condition of same grinding fineness，material with more micro cracks，iron mineral content in fine grained is more higher，particle size distribution is more reasonable at the same time，but the growth trend with the increase of grinding fineness gradually lower.The experimental results can provide theoretical basis for reducing the grinding cost of Jidong magnetite to save energy and to reduce the cost and increase the efficiency.

Key words: High pressure roller mill breakage, Jaw crushing, Microcrack, Bond Ball Milling Work Index