The invention relates to a modified sulfur/carbon coated lithium nickelate cathode material and a preparation method thereof. The modified sulfur/carbon coated lithium nickelate cathode material is prepared from the following components in parts by weight: 27 parts of sulfur/carbon composite material, 70 parts of active material, 5 parts of functional material, 8 parts of conductive material and 8 parts of binding material, wherein the functional material is 60% lithium iron nitrate solution; the cathode material is lithium nickelate; the conductive agent is flake graphite. The defect of failure of lithium ion batteries caused by self-discharge of protection boards is overcome by adopting the modified sulfur/carbon coated lithium nickelate cathode material, thus improving self-discharge of the whole battery pack, achieving the aim of prolonging the lithium battery storage time and ensuring that the lithium batteries can be stored for a longer time under the condition that users do not charge the electric appliances after using the electric appliances.