The invention provides a method and a device for preventing people in a vehicle from suffocation. The method comprises the following steps: opening an oxygen concentration sensor under the conditions that an engine is started and vehicle windows are closed; detecting an oxygen concentration value in the vehicle by the oxygen concentration sensor; and if a current oxygen concentration value is lower than a pre-set value, carrying out vehicle window opening operation and driver reminding operation. According to the method provided by the invention, the people in the vehicle are prevented from suffocation when the engine is started and the vehicle windows are closed.