Disclosed are a device and a method for bonding an auxiliary secondary barrier for an LNG storage tank. The device for bonding an auxiliary secondary barrier includes: a frame; a driving unit, a portion of which is arranged in the frame, and which enables the frame to move on an upper heat insulation board corresponding to an exposed portion of a main secondary barrier; an adhesive applying unit arranged in the frame to apply an adhesive on the exposed portion; an auxiliary secondary barrier supply unit arranged in the frame to supply an auxiliary secondary barrier on the adhesive applied on the exposed portion; and one or more heating unit arranged in the frame to heat at least one of the exposed portion to which the adhesive contained in the adhesive applying unit is to be applied and the auxiliary secondary barrier to be supplied on the applied adhesive.