Abstract: A corner joint of a frame for fixing a solar panel disposed between two adjacent frame pieces of the frame includes an L shaped member and a sheath. Two ends of the L shaped member separately extend to one corresponding frame piece of the two adjacent frame pieces to form an extending arm plugged into a latching slot defined in an end of the corresponding frame piece. The L shaped member further includes a bending portion defining a mortise extending to the extending arm. The sheath includes two adjacent joint surfaces for abutting the two adjacent frame pieces. The sheath defines an upper receiving space and a lower receiving space therein. The upper receiving space and the lower receiving space are separately exposed from the joint surfaces. The upper receiving space and the lower receiving space are configured for receiving a corner of the solar panel and the bending portion, respectively.