The invention discloses an insulation material for cables and a preparation method thereof, belonging to the technical field of insulation materials. The invention is characterized in that the insulation material for cables is composed of the following components in parts by weight: 100-200 parts of high-polymer resin, 50-80 parts of polyethylene, 20-40 parts of flame retardant, 15-20 parts of white carbon black, 10-20 parts of calcium carbonate, 8-15 parts of antioxidant, 5-10 parts of lubricant and 2-8 parts of dispersing agent. The flame retardant is one or combination of more of zirconium oxide, magnesium hydroxide and zinc borate. The preparation method of the insulation material for cables comprises the following steps: weighing the raw materials, mixing, and carrying out extrusion granulation to obtain the insulation material. The mixed flame retardant is adopted, and the dispersing agent is added to improve the problem of flame retardant accumulation due to the addition of the single metal oxide flame retardant, so that the obtained material has favorable insulating property and favorable flame-retardant effect. The preparation method has the advantages of simple technical process and controllable technological parameters.