We briefly review methods for determining minimum miscibility pressure (MMP). We propose a modified multiple mixing cell method for determining the minimum miscibility pressure, based on the variation in the tie-lines at different pressures. First using the conventional multiple mixing cell method, we calculated the tie-line length, studied the tie-line pattern, and found the pressure-dependent critical points. Then we proposed some steps to improve the existing algorithm. The results obtained using the modified method are compared with the results of other methods. We have established that our algorithm can solve the problem of the complexity of searching for key tie lines, as is done in the calculation by the conventional mixing cell method, and thus our algorithm ensures that we find an accurate value of the MMP.