Abstract: Hindered phenohc antioxidants triethylene glycol bis-3(3-tert-butyl-4一hydroxy-5methyl phenyl) propionate(Irganox245)and n-octadecyl-(3-(4-hydroxy-3，5一di-tert-butyl-phenyl ) propionate(Irganox1076 ) were separately compounded with sulfur-containing antioxidant dilauryl thiodipropionate (DLTP).the compounded antioxidants were introduced as emulsions into acrylonitrile-butadiene-styrene (ABS) emulsion. The stabilization effect of the antioxidants was studied by determining the aging time of yellow, thermal weight loss rate，and yellowness index. It showed that a strong synergistic effect was exhibited by the compounded antioxidant of Irganox245 and DL}CP, however, no synergistic effect was observed for Irganox1076 and DLTP. through the investigation, it was confirmed that the
degradation of ABS began with the destruction of double bonds followed by the formation of hydroperoxides, carbonyl，and alkyloxy compounds.

Key words: acrylonitrile-butadiene-styrene copolymer, antioxidant, synergistic mechanism, thermal oxidative degradation mechanism