A system comprising a quick coupler connection system for a construction machine and an attachment, the quick coupler connection system comprising: a quick coupler main body that includes left and right quick coupler bodies (110, 120) facing each other at left and right sides and connected to each other by a connection plate on rears thereof, an actuating cylinder rotatably disposed inside the left and right quick coupler bodies (110, 120) and having an actuating rod disposed on a top thereof and coupled to a connection block of a moving jaw of an attachment by a coupling pin, and a first connection pin and a second connection pin connecting the left and right quick coupler bodies (110, 120) and a cylinder connection pin rotatably supporting the actuating cylinder; the attachment capable to be detachable coupled to the quick coupler main body and having the moving jaw being rotatable with respect to a fixed jaw; and guides disposed on inner surfaces of the connection block and guiding pin assembly positions of the connection block and the actuating rod when the moving jaw is rotated, wherein a lower portion of the actuating cylinder operating the moving jaw is shaft-coupled to the quick coupler main body and the system being characterized by a supporting assembly that supports the actuating cylinder to prevent rotation of the actuating cylinder before the actuating rod of the actuating cylinder is coupled to the connection block of the moving jaw is provided, the supporting assembly has a fixed block fixed on an outer surface of a cylinder tube of the actuating cylinder on a side, a supporting block detachably coupled to the fixed block on a side by a bolt and having a coupling protrusion having a fixing hole, and supporting holes formed through the left and right quick coupler bodies (110, 120) such that a supporting pin disposed through the fixing hole is pin-coupled therein. a quick coupler main body that includes left and right quick coupler bodies (110, 120) facing each other at left and right sides and connected to each other by a connection plate on rears thereof, an actuating cylinder rotatably disposed inside the left and right quick coupler bodies (110, 120) and having an actuating rod disposed on a top thereof and coupled to a connection block of a moving jaw of an attachment by a coupling pin, and a first connection pin and a second connection pin connecting the left and right quick coupler bodies (110, 120) and a cylinder connection pin rotatably supporting the actuating cylinder; the attachment capable to be detachable coupled to the quick coupler main body and having the moving jaw being rotatable with respect to a fixed jaw; and guides disposed on inner surfaces of the connection block and guiding pin assembly positions of the connection block and the actuating rod when the moving jaw is rotated, wherein a lower portion of the actuating cylinder operating the moving jaw is shaft-coupled to the quick coupler main body and the system being characterized by a supporting assembly that supports the actuating cylinder to prevent rotation of the actuating cylinder before the actuating rod of the actuating cylinder is coupled to the connection block of the moving jaw is provided, the supporting assembly has a fixed block fixed on an outer surface of a cylinder tube of the actuating cylinder on a side, a supporting block detachably coupled to the fixed block on a side by a bolt and having a coupling protrusion having a fixing hole, and supporting holes formed through the left and right quick coupler bodies (110, 120) such that a supporting pin disposed through the fixing hole is pin-coupled therein.