Abstarct: In underground mines the composition of the mine air is constantly changes duo to the workmen breathing, blasting, infiltration of the harmful gases and mineral gas permeation. Ventilation is one of the most important work in underground mining. Incorrect ventilation design causes serious danger to the workmen and mine equipment. There is several method to design and modelling the ventilation in underground mines, today numerical modelling is common. In this thesis first, the ventilation system in one of the eastern Alborz coal mines (Bornaki) was examined then according to the current conditions of the mining, the required air flow intensity and type of ventilator were introduced and the economic analysis was done. baxsed on the results, the total flow intensity of mine network was calculated 10.9 (m3/s) and an air regulator valve has been used to adjust the flow. To venting this mine the WATS 11 ventilator with 60 degree wing angle is recommended.