The present invention discloses a method of controlling fresh air of a subway air conditioner, comprising the steps of: obtaining a passenger flow in a station for a current control cycle; determining a fresh air volume demanded by the station for the current control cycle based on the passenger flow and a preset fresh air volume; wherein the preset fresh air volume is a fresh air volume required by a passenger; and if the fresh air volume demanded by the station is greater than a preset threshold value of the fresh air volume, controlling the station according to the station-demanded fresh air volume fresh air output from the fresh air machine. The new air control method for railway air conditioning of the present invention can effectively save energy consumption while ensuring good air quality.