The present invention relates to a sterilizer using an impermeable sealed container and a sterilization method thereof, and more particularly, to a sterilizer using an impermeable sealed container and a sterilization method thereof, the sterilizer being capable of diagnosing residual moisture to improve sterilization reliability and increase sterilization efficiency, and directly being connected to a vaporizer. More specifically, the present invention relates to a technique for solving the problems of taking a long time to sterilize and inefficiency in removing and purifying a sterilant that remains after the sterilization is completed, and for improving the problems of difficulty in ensuring sterilization reliability and inefficiency in using a sterilizer due to the same drying process irrespective of actual residual moisture.