The invention relates to a halogen-free flame retardant HIPS (High Impact Polystyrene) plastic modified material and a preparation method thereof. The halogen-free flame retardant HIPS plastic modified material comprises the following materials in parts by weight: 40-45 parts of HIPS, 35-40 parts of MPPO (Modified Polyphenylene Oxide), 5-7 parts of halogen-free flame retardant, 3-5 parts of red phosphorus powder, 3-5 parts of K resin, 3-5 parts of SBS (Styrene Butadiene Styrene), 0.3-0.5 part of lubricating agent, 0.2-0.5 part of white mineral oil and 0.5-2 parts of carbon black powder. The halogen-free flame retardant HIPS plastic modified material not only has good flame retardation and strong safety, but also has good mechanical performances including tensile strength and the like; a television enclosure, which is manufactured by the halogen-free flame retardant HIPS plastic modified material, has stronger impact resistance and a long service life, and can be recycled. The processing materials MPPO and HIPS are mainly reclaimed materials, so that the cost of the modified HIPS plastic material is greatly lowered. The halogen-free flame retardant HIPS plastic modified material is free of halogen, environment-friendly and capable of generating great environment-friendly benefits. Besides, the preparation method of the halogen-free flame retardant HIPS plastic modified material is simple to operate, less in needed equipment and low in production cost.