Abstract: In order to study the change rule of smoke under the influence of fire source scale and airflow velocity when fire occurs in intake airway in fully mechanized working face. Using PDS fire simulation software to simulate the variation of the CO concentration, temperature and visibility under the different fire source scales and airflow velocity. The five fire sources scales were 1 MW, 2 MW, 5 MW, 10 MW and 20 MW respectively. The eight kinds of airflow velocity were in the range from 1.0 m/s to 2.4 m/s. The results show that:(1) as the size of fire source increases, CO concentration increases, the time required for CO concentration distribution to enter the stable stage is prolonged, the time required for temperature rise to reach the stable stage is prolonged, and the speed of temperature drop is accelerated; (2) with the increase of airflow velocity, the time required for CO concentration distribution to enter the stable stage is shortened, the CO concentration decreases in the stable stage, and the temperature in return airway rises; (3) with the increase of airflow velocity, smoke spread faster, and visibility narrows at the exit; (4) as the airflow velocity increases, CO concentration and temperature in the upper windward side of the fire source decrease, and the distance of smoke rollback shortens, the smoke does not rollback after exceeding the critical airflow velocity. The study can provide guidance for underground workers to escape safely during a fire.