A pyrolysis gas chromatography-mass spectrometry with silica as dispersant for sample preparatio was developed for the quantitative analysis of blend ratio of polycarbonate(PC) to acrylonitrile-butadiene-styrene copolymer(ABS).The samples were dispersed with silica after freeze fracturing,then weighed carefully and injected.The pyrograms of the samples were obtained at a pyrolysis temperature of 600 ℃.The characteristic peak of styrene in thermally decomposed polyester was selected as the quantitative peak for determination of the blending ration of PC and ABS in PC/ABS blend.A series of content known PC/ABS blend standards were prepared using silica as dispersant.Results showed that there were good linear relationships between styrene peak area and ABS concentration in the range of 0.06-20 g/kg(corresponding to PC∶ABS ratio of 99.7∶0.30-0∶100),with their correlation coefficient(r2) of 0.994.The detection limit(S/N=5) of the method for ABS was 0.06 g/kg(corresponding a PC to ABS ratio of 99.7∶0.30).The method was applied to the PC/ABS blend samples with known bending ratios.The recoveries ranged from 95.3% to 103% with relative standard deviations(RSDs,n=3) of 1.1%-3.8%.The method is simple,convenient and accurate,ant it is suitable for the analysis of PC/ABS blending ratio in the full range.