A method for pasteurizing freeze dried food comprises: 1) Determining the corresponding sterilization temperature according to the food to be sterilized, and determining the target water activity at the sterilization temperature; 2) Cooling the food to a temperature corresponding to the type of the food; 3) Removing the air from the sterilization chamber using a vacuum pump; 4) Introducing water vapor into the sterilization chamber, adjusting the steam flow rate after the food temperature reaches the sterilization temperature, and maintaining the food temperature at the sterilization temperature for a specific duration and ceasing the introduction of water vapor; 5) Capturing steam from the sterilization chamber and reducing the pressure in the chamber; 6) After the pressure in the chamber reaches or approaches the water saturation pressure corresponding to the cooling temperature prior to sterilization, charging clean air into the chamber until the vacuum state is released, and removing the food.