The invention belongs to the technical field of sewage treatment and inorganic fiber modification, and relates to surface modification of basalt fibers, in particular to a preparation method of a hydrophilic chitosan modified basalt fiber support. The method comprises the following steps: firstly, etching is performed on the surfaces of the basalt fibers with alkali liquor, and the fibers are washed with deionized water to be neutral, dried and activated; then physical coating is performed, chitosan is taken as a modifier, the etched and dried basalt fibers are soaked in a chitosan solution, and the hydrophilic polymer modified basalt fiber support material is prepared. The method is simple in process, convenient to operate, suitable for industrial production and easy to popularize. The prepared modified basalt fiber support can keep original properties such as high specific surface area, excellent mechanical property, acid-base resistance and the like of the basalt fibers; a contact angle can be reduced, hydrophilicity of the basalt fibers is improved, adhesion of microbes on support surface is promoted, growth of a biofilm is accelerated, a biofilm formation period is shortened,capacity and activity of the microbes are increased, water purification efficiency is increased, and higher reuse rate is realized.