Wax precipitation is a series problem that caused problems in production, processing and traortation in the industry. In order to prevent drastic economic consequence a suitable knowledge of the wax behavior should to be investigated. Waxes precipitate below the wax appearance temperature. In this paper, Multi solid and Solid solution model are considered. Liquid and vapor phase is described by Modified Peng Robinson equation of state which it is described heavy hydrocarbons well. Fugacity of solid phase is calculated indirectly by fugacity of pure liquid phase. In this approach, crude oil is divided into five pseudo components using the SARA test results. Solubility parameters are calculated by SRK equation of state and composition of components are calculated by Rachford Rice equation. In this paper is used Genetic Algorithm to improve accuracy of results in WAT and wax weight percentage. The average deviation of WAT are 0.11 and 0.15 % in multi solid and solid solution model respectively, also the average deviation of wax weight percentage are 10.32 and 5.8 % in multi solid and solid solution model, respectively. Results are showed solid solution model is predicted better than multi solid model, because optimized parameters in this model are more effective and have direct influence in this approach. Models are remarkable accuracy with experimental data. Asphaltene is omitted in five crude oils to evaluated influence of Wax weight percentage and WAT. Results are represented Asphaltene increasing WAT and Wax weight percentage.