An improved variable frequency ventilation automatic control logic is introduced, which is suitable for the complex engine room ventilation system of large merchant ships. On the basis of the widely used variable frequency fan control based on the exhaust temperature signal and pressure signal in the engine room, several Temperature Transmitters(TT) are supplemented to monitor and pay special attention to the temperature of key cabins such as the generator room and oil purifier room. The operation control logic of variable frequency fan is simplified, the control logic of variable frequency fan in the engine room is more concise and efficient on the basis of saving energy and reducing consumption, and the robustness of ventilation system is greatly improved, which is of reference significance for the variable frequency ventilation control in the complex engine room of other ships.