Disclosed is a method for manufacturing gas cylinders. The disclosed method for manufacturing gas cylinders comprises: a) a step of producing a liner using a liner blower machine; b) a step of applying an adhesive to the threads of the produced liner; c) a step of coupling a bushing to the threads of the liner; d) a step of leaving the liner having undergone step c) for 30 minutes to 2 hours at room temperature so as to naturally harden the adhesive; e) a liner-flaming step of heat-treating the outer surface of the liner with plasma; f) a step of coupling a shaft to the liner; g) a winding step of mixing multiple fiberglass strands with a resin and a hardening agent, and wrapping the mixture around the outer surface of the liner; h) a dry-hardening step of drying the cylinder made of the composite material and having undergone the winding step for 70 to 90 minutes at a temperature of 70°C to 90°C; i) a cooling step of leaving the cylinder made of the composite material for 15 to 40 minutes at room temperature so as to lower the surface temperature of the cylinder having undergone the dry-hardening step to a level of 35°C or lower; j) a step of separating the shaft from the cylinder made of the composite material; k) a step of assembling a valve to the bushing installed in the cylinder made of the composite material; and l) a step of checking the state of the gas cylinder including the cylinder made of the composite material.