The invention relates to a preparation method of a flexible cable sheath material, belonging to the technical field of cable materials. The preparation method comprises the following steps: evenly mixing the following raw materials in parts by weight: 40-55 parts of a rubber base material, 5-15 parts of silicone rubber, 3-6 parts of tackifying resin, 1-3 parts of an anti-aging agent, 4-7 parts of a reinforcing agent, 5-8 parts of a filling agent, 2-4 parts of a vulcanizing accelerator, 3-5 parts of a vulcanizing agent, 3-5 parts of a plasticizer, 3-5 parts of an active agent and 3-6 parts of an organic solvent, feeding a twin-screw extruder with the mixture for extruding and granulating, enabling the obtained granules to enter a hot air drier, and drying to obtain the cable sheath material. The silicone rubber is added into the cable sheath material, so that the problems that the flexible cable material is lower in elasticity and tensile property can be solved; furthermore, white carbon black filler is modified, so that the problem that the cable material is poor in solvent resistance due to the addition of the white carbon black filler can be solved; the prepared cable sheath material has the advantages of being good in tensile property, insulating property and solvent corrosion resistance.