The work aims to determine the content of ethylbenzene and styrene in plastic products by gas chromatography internal standard method to provide reference for the determination accuracy of ethylbenzene and styrene in plastic products. The content of ethylbenzene and styrene in plastic products was determined by gas chromatography internal standard method according to GB 31604.16-2016. According to the corresponding measurement model, the sources of main influencing factors of the uncertainty were analyzed, and the relative standard uncertainty introduced by each influencing factor was evaluated. The expanded uncertainty of measurement of ethylbenzene and styrene in plastic products was (23.83±1.50) mg/kg and (23.90±1.26) mg/kg (P=95%, k=2) respectively. The results show that the preparation of mixed standard working solution, repeated measurement of sample and gas chromatograph are the main factors affecting the uncertainty of ethylbenzene and styrene content measurement. Measuring tools with high accuracy and appropriate range shall be selected. Periodic check and verification of gas chromatograph shall be strengthened. The proficiency level of experimental personnel shall be improved. The measurement uncertainty shall be further reduced, so that the measurement results would be more accurate and reliable.