Flash calculation is an important process in the industry to study the phase equilibrium. The mathematical modeling of flash calculation is getting significant in industrial problem solving. In this research, Soave Redlich Kwong (SRK) equation is used to calculate the thermodynamic properties of the mixture in the critical region. From the literature, experimental data is selected to study the behavior of four different binary
mixtures. Mathematical modeling was performed to study the behavior of pressure with a mole fraction of the liquid phase and vapor phase mixture at equilibrium. An initial guess of K-values is done by using Wilson
equation. The equilibrium is established when the convergence is occurring on applied condition of fugacity coefficient. The behavior is compared with the experimental data present in literature which show that this
isothermal flash calculation almost follows the same trend like as experimental data.