With Braun K10 equation as the thermodynamic method, ethylene quench system was simulated using software PROM. Instead of pseudo-components, the pyrolysis oil was characterized by real components. Real components were selected from paraffin, naphthene and aromatic groups (PNA) for each cutting interval of true boiling point (TBP) curve. Compositions of PNA components in each interval were supposed to be the same with that in whole pyrolysis oil. Simulation results was consistent with measured data and better than using pseudo - components, which proved that the new approach could be an effective way to calculate quench system. (c) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.