The invention discloses a formula of halogen-free flame retardant PP (polystyrene). The formula of the halogen-free flame retardant PP comprises 60-70 parts of PP AW 564, 20-25 parts of MPP, 10 parts of talcum powder with a high mesh count, 1-3 parts of dispersing master batch, 0.2-1 part of antioxidant, 0.5-1 part of lubricating agent and 0.5-1 part of other processing agents. The invention also discloses a preparation method of halogen-free flame retardant PP. The preparation method comprises the following steps of: 1, selecting and mixing the PP AW 564, adding silicone oil and stirring, and then adding the antioxidant, the lubricating agent and the other processing agents and stirring, then adding the dispersing master batch and stirring, and finally adding the MPP and the talcum powder with a high mesh count and stirring to obtain the semiproduct of halogen-free flame retardant PP; and 2, extruding the prepared semiproduct, cooling and cutting into grains to finally obtain the finished product of halogen-free flame retardant PP. The prepared halogen-free flame retardant PP material has the advantages of favorable appearance, high temperature resistance, no drippage, no precipitation and light specific weight, has the effect of low smoke zero halogen and better meets the requirement of environmental protection.