Miscible and/or near miscible gas injection processes are among the most widely used enhanced oil recovery techniques. The successful design and implementation of a miscible gas injection project is dependent upon the accurate determination of minimum miscible pressure (MMP), the pressure above which the displacement process becomes multi-contact miscible. Analytical methods, which are inexpensive and quick to use, have been developed to estimate MMP for complex fluid characterizations. However, many problems still existed in the analytical calculation, which will lead to the failure of calculation, or wrong result. This paper shows how the initial tie line could be calculated when the component of injection gas doesn’t included in the crude oil. And moreover, how to get a complete set of initial value for the equations of crossover tie lines, and the influence of EOS for the result of key tie lines is analyzed simultaneously.