Underground coal mine development is commonly accompanied by increasing ventilation resistance and changing airflow requirements, making the selection of a suitable main ventilation fan progressively more challenging throughout the mine life. This study presents the design of the ventilation system and the selection of the main ventilation fan for Block 3 of the Parvadeh 4 coal mine using a combination of ventilation network analysis and three-dimensional airflow simulation in VentSim. Airflow requirements for development headings and mechanized longwall panels were determined in accordance with the Iranian Coal Mine Safety Regulations, considering methane dilution, dust control, blasting gases, and workforce requirements. The VentSim model was verified by independent pressure-loss calculations based on the Atkinson equation. Three representative development stages covering a 15-year mine life were analyzed to evaluate airflow distribution, ventilation resistance, and fan operating conditions. The results showed that the total ventilation pressure loss increased from 795 Pa in Stage I to 1032 Pa in Stage II and then to 1868 Pa in Stage III as the ventilation network grew. With a design airflow of about 107 m³/s, allowing for a 20% design allowance, the ventilation requirements for the whole life of the mine were met. The fan performance was evaluated and it was found that the single motor was sufficient for the first two development phases and the dual motor operation was required for the last development phase due to the increase in network resistance. Among the evaluated alternatives, the FBCDZ No. 24 twin-motor axial fan provided the most suitable operating range and maintained high efficiency under all planned operating conditions. The proposed procedure provides a practical approach for ventilation planning and main fan selection in mechanized underground coal mines.