A method and system for realizing universal anti-forgotten sensing device for in-vehicle passengers, which are designed to improve the accuracy of anti-forgotten recognition for children in a vehicle. For the method and system for realizing universal anti-forgotten sensing device for in-vehicle passengers, the method comprises: determining whether a vehicle state event pertains to a predetermined alarm event, if so, determining whether the current in-vehicle environment satisfies the situation in which a human body moves and someone makes a sound, and/or the current in-vehicle environmental data exceeds a predetermined threshold range, and if so, determining that someone is forgotten in the vehicle and sending alarm information; otherwise, performing no processing. The system is applicable to all types and brands of vehicles without any need for modification to the vehicle, and the system is truly plug and play, and the cost is greatly reduced.