The invention discloses a corner enhancing connecting device of a door and a window sash and a connecting method of the device. The problems that the corner connection of the door and the window sashis prone to deformation, and the sealing performance is poor in the prior art are solved. The corner enhancing connecting device of the door and the window sash comprises steel liners correspondinglyarranged in a first sash proximate matter and a second sash proximate matter, wherein connecting and fixing pieces are arranged in the steel liners, and the steel liners are connected with the connecting and fixing pieces through L-shaped enhancing pieces; and the lower parts of the connecting and fixing pieces are connected through a connecting box, and the connecting box is matched with the connecting and fixing pieces. According to the corner enhancing connecting device of the door and the window sash and the connecting method of the device, the strength of connecting corners of the door and the window sash can be effectively enhanced through the connecting and fixing pieces, the connecting box and the L-shaped enhancing pieces, the strength of the door and the window sash can be improved under the condition that the appearance and other basic properties of the door and the window are not affected, the performance degradation of the door and the window caused by excessive deformation is basically avoided, the tearing phenomenon of the corners of the door and the window sash is eliminated, and the device and the method have higher popularization value.