The invention relates to a method for preparing an olivine type lithium iron phosphate positive electrode material, and belongs to the technical field of lithium ion battery electrode materials. The method comprises the steps: at room temperature, adding water to lithium carbonate, anhydrous iron phosphate and a carbon source and carrying out ball milling mixing, wherein the solid content is 30-70%, the molar ratio of Li to Fe to P is x to 1 to 1, 1<=x<=1.05, anhydrous iron phosphate is a mixed phase of monoclinal structure iron phosphate and tripartite structure iron phosphate with the molarratio of y:(1-y) or a mixed phase of hexagonal structure iron phosphate and tripartite structure iron phosphate with the molar ratio of y:(1-y), and 0<=y<=0.8; and after the ball-milled material is dried, sintering in a nitrogen atmosphere to obtain the olivine type lithium iron phosphate positive electrode material. The invention provides the method comprising that anhydrous iron phosphate havingspecific crystal structure is used as a raw material for preparing lithium iron phosphate, so as to further optimize the synthesis and performance of LiFePO4.