When a cold rolled strip is being treated in a continuous annealing furnace which is full of protective gas,the gas tightness of the furnace body,the connected facilities and the gas channels become an important indicator that directly affects the product’s surface quality and shows the technical level of the design,the manufacture and the installation.By considering the problems of the gas tightness of a vertical annealing furnace in the installation and maintenance,this thesis evaluates the gas tightness indicator and gas tightness related level of the furnace body and the circulation duct,while studying and analyzing the technologies of negative-pressure leak detection and sealing. When a cold rolled strip is being treated in a continuous annealing furnace which is full of protective gas, the gas tightness of the furnace body, the gas tightness of the furnace body, the gas tightness of the furnace body level of the design, the manufacture and the installation. By considering the problems of the gas tightness of a gas annealing furnace in the installation and maintenance, of the evaluations of the gas tightness indicator and gas tightness related level of the furnace body and the circulation duct , while studying and analyzing the technologies of negative-pressure leak detection and sealing.