Migration experiments with expanded polystyrene were performed in one-sided contact with distilled water and 95%(V/V) ethanol water as the food simulants at various temperatures(25, 45 and 65 ℃) and the styrene migrating to the food simulants was tested from 1 to 240 h. The results show that styrene could hardly be measured in distilled water and the amount of styrene in the 95%(V/V) ethanol water was obviously greater than that of in distilled water. The diffusion coefficients of styrene in expanded polystyrene were 5.08×10-9,1.29×10-8 and 6.78×10-8 cm2/s at various temperatures(25,45 and 65 ℃) and the corresponding activation energy of the migration process was 53.9 kJ/mol.