The invention discloses a method for crushing an iron ore, comprising the following steps of primary crushing, ore washing and high pressure roller-milling, wherein the step of primary crushing uses a multi-level sieving cycling closed loop for crushing, and the step of high pressure roller-milling also uses a closed loop method; compared with the traditional crushing process flow, the process uses the production method of high pressure roller-milling scattering sieving closed loop process flow so that the range of the particle size of a final product is ensured to be narrow and the size thereof is uniform; the material in the final product of the ore is fully rolled and pressed by a high pressure roller miller so as to reduce the fineness of the material to the maximum degree, reduce theBond index of the milling material, efficiently decrease the procedure energy consumption and steel ball consumption in milling operation and improve the selection index; moreover, the stable production process is ensured, the energy is saved and the consumption is reduced, much crushing and less milling are really realized, and the production capability of an ore factory is greatly improved.