The invention relates to a method for preparing lignocellulose-II crystal form nanofibers through grinding. The method includes the steps: (1) removal of part of lignin, (2) strong base solution treatment, (3) removal of residual lignin, and (4) primary grinding by a machine. The method has the advantages that through primary grinding, the process is simple and convenient, energy consumption is low, yield is increased, and operation difficulty and preparation cost are reduced; the obtained nanofibers are the lignocellulose-II crystal form nanofibers, uniform diameter distribution is achieved,and thermodynamic property is stable; a wood flour mixing solution is treated by sodium chlorite and glacial acetic acid to remove part of the lignin in wood flour, the residual lignin in the wood flour can effectively inhibit large-scale cellulose conglobation caused by strong base treatment, follow-up mechanical treatment is conducted, and the yield of the lignocellulose-II crystal form nanofibers obtained after primary grinding is increased remarkably to 80-85%.