Abstract: A method for predicting naphtha composition based on the conventional physical properties was established. Based on the data base of RIPP, 54 real components were chosen to represent the composition of naphtha, which is divided into 4 groups: N-paraffins, iso-paraffins, naphthenic and aromatics. A set of simulation equations were built using conventional properties of density, refractive index，group composition，and Engler distillation curve of 4 groups to get the mass fractions of 54 components and then compared with the measured results. The results show that the calculated compositions agree well with the measured results. The calculation average error for corresponding normal alkanes, iso-alkanes, cyclanes is 6.6%, 8.5%, 5.9%, respectively. The error of alkanes, iso-alkane and cyclanes contents in C6-C11 is 3.2%, 5.2%, 4.4%, respectively. The above results demonstrate that the established model equations can reflect well the hydrocarbon distribution of straight-run naphtha.