The invention relates to an existing curtain wall detachable closed cavity type cross beam connecting device. The device is mounted on the two sides of a cross beam correspondingly, is used for detachable connection of the cross beam and stand columns, and comprises a fixing assembly, cross beam connecting pieces mounted on the two sides of the cross beam, stand column connecting pieces mounted onthe stand columns on the two sides, and middle connecting pieces connected with the cross beam connecting pieces and the stand column connecting pieces correspondingly, wherein the shapes and the configurations of the stand column connecting pieces and the shapes and the configurations of the middle connecting pieces are the same, and the fixing assembly is used for fixing connected cross beam connecting pieces, stand column connecting pieces and middle connecting pieces. Compared with the prior art, the existing curtain wall detachable closed cavity type cross beam connecting device has theadvantages that safety and reliability are achieved, and detaching is convenient and the like.