The present invention discloses an interior air quality monitoring and ventilation control method and system for a train. The interior air quality monitoring and ventilation control method for the train comprises: acquiring multiple groups of interior and exterior air quality detection data; acquiring interior and exterior air comprehensive evaluation index Q0 and Q1 by using the experimental data; training an exterior fresh air volume control model if Q0≥Q1, or else training an interior air purification control model; detecting the interior and exterior air quality detection data; acquiring the interior and exterior air comprehensive evaluation index Q0 and Q1 by using the detection data; if Q0≥Q1, calling the exterior fresh air volume control model to obtain the required ventilation volume level and controlling a ventilation system with the output result; otherwise, calling the interior air purification control model to obtain the required ventilation volume level and air purification device power level, controlling the ventilation system and the air purification device with the output results. The present invention can apply suitable ventilation control strategies according to different degrees of air quality, to achieve a health guarantee for the interior air quality of the high-speed train under the conditions of energy conservation and environmental protection.