Abstract: The flame-retardant ABS was prepared by combination of phenolic resin (PF) with several types of phosphates such as triphenyl phosphate (TPP), bisphenol A bis(diphenyl phosphate) (BDP) and isopropylated triphenyl phosphate (IPPP). The effects of the type and dosage of phosphates on the flame retardant properties of ABS were investigated, and the flame retardant mechanisms were studied by FTIR and SEM. The results indicated that phosphates could affect the flame retardancy of ABS by physical interference at different loading but by chemical interference with different types. The chemical interference had a strong catalytic effect on physical interference.