A method for manufacturing a secondary battery includes a cap assembly manufacturing step to provide a cap assembly having a top cap having a top hole, a safety vent having a vent hole, and a CID filter having a CID hole; an electrode assembly and electrolyte accommodating step of accommodating an electrode assembly into a can and injecting an electrolyte; a preliminary battery manufacturing step which comprises a disposing process of disposing the cap assembly above the can and a coupling process of coupling a positive electrode tab provided in the electrode assembly to a bottom surface of the CID filter of the cap assembly; an activation step of charging and discharging the preliminary battery; and a gas discharging step of pressing downward the positive electrode tab in contact with the CID filter, thereby opening the CID hole and discharging a gas generated inside the can.