A novel halogen-free double hydroxyl phosphate melamine octomolybdate (BTOCPMOM) was synthesized from pentaerythritol, phosphorus oxychloride, melamine and ammonium heptamolybdate through complex formulation of pentaerythritol phosphate and melamine octomolybdate. The synthesis optimized conditions determined by single factor method were: reaction temperature was 100℃ and reflux time was 6h, and the yield of product reached 88.3%. Molecular structure of BTOCPMOM was identified by FTIR and elemental analysis. The thermogravimetry analysis (TGA) and flame retardant performance test showed that the synthetic products showed good thermal stability and eximious char-forming feature. The addition of the BTOCPMOM in Polypropylene as the ratio of w(BTOCPMOM):w(PP)=30:70 could reach the limiting oxygen index (LOI) value of 35.2% and the flame retardancy of UL-94V-0.