The invention provides a method for preparing a cathode material of a lithium iron phosphate lithium-ion battery, and relates to a method for preparing the cathode material of a lithium-ion battery. The invention solves the problems of low specific capacity, poor loop stability and high cost in the preparation of the cathode material of the lithium iron phosphate lithium-ion battery by the prior solid phase method t. The method comprises the following steps: firstly rolling lithium hydroxide, ferrous oxalate, ammonium dihydrogen phosphate, conductive agents and dispersants by a double-roll blender mill, crushing, sintering, rolling after adding pitch, crushing and resintering; or firstly extruding the lithium hydroxide, the ferrous oxalate, the ammonium dihydrogen phosphate, the conductive agents and the dispersants by a double-screw extruder, crushing, sintering, rolling after adding pitch, crushing and resintering. Compared with the materials using sucrose as the carbon source, the cost of the cathode material of the lithium iron phosphate lithium-ion battery is reduced by 40-55%, the specific capacity is 100mA.h/g-120mA.h/g, the cyclical stability is good, so the prepared cathode material can be applied to the batteries used by mobile telephones, notebook computers and electrocars.