Auxiliary ventilation refers to the systems that are used to supply fresh air to the working faces in dead end including the use of a push-pull arrangement. There are many advantages of using such a system when compared to other methods. It has been shown that for headings longer than 30 m, auxiliary fans are the only practicable means of delivering the required air quantities. Besides air quantities, air quality is another critical issue for evaluating the ventilation efficiency in underground mines. Forcing and exhausting ducts used in the push-pull system are closely associated with the ventilation efficiency. This paper focuses on the efficiency evaluation for a push-pull ventilation system by using two methods, the dead zone and the mean age of air. By using the CFD technology, the air velocity and air quality are calculated and compared in four different cases. The results of evaluation will be identical by using these two methods. It is concluded that in the push-pull ventilation system, the position of the forcing duct plays a major role on the ventilation efficiency. Also, when the forcing duct position is determined, there must be a particular position of the exhausting duct to provide best ventilation efficiency.