The invention discloses a method for preparing a composite material for a cathode of a lithium ion battery, comprising: ultrasonically dispersing polytetrafluoroethylene in water, then adding carbon material and sodium dodecyl benzene sulfonate, ultrasonically dispersing, adding manganese sulfate and ammonium persulfate, reacting in a high pressure reaction vessel, washing and drying a product to obtain a manganese dioxide-carbon material-polytetrafluoroethylene composite material. The method is simple and reliable. The price is low. A specific capacity of lithium extraction of the prepared material is very high. The method is provided for producing a high-performance lithium ion battery cathode material.