Gas sterilization which complements the steam sterilization is used for the materials which are unstable under high temperature and moisture or items to which the steam sterilization is inapplicable for the structural reasons, therefore it is essential for medical institutions employing precise and delicate medical devices to use this kind of low temperature sterilizer. This sterilizer uses the gas mixtures with Ethylene Oxide (EO) and Freon or Carbon Dioxide (CO2) as sterilant, and is a typical large EO Gas sterilizer which is effective to sterilize a large number of medical instruments or bulky packages at a time by adopting a large sized chamber, and it has a good performance of vacuuming, strong durability and low noise. It can use the two gas cylinders in successive automatically by the built-in program, and displays the cycle processing situation on the message center, therefore the possible problems such as cycle stop and gas leakage etc due to the replacement of gas cylinder can be prevented. The optional type sterilizer adopted a wide touch screen color LCD is able to operate the sterilizer on the touch screen by one touching, to monitor the cycle processing in real time on it and to manage the occurred troubles quickly during operating. The built-in panel printer prints out the cycle performance record for securing the traceability afterwards.