To provide a structure and a method for repairing an existing channel, which eliminate the risk that water may get into a space between a panel plate arranged on a bottom surface of the existing channel and the bottom surface, from both side portions.

In a structure for repairing an existing channel 100, a side surface of the existing channel 100 and both side portions of a bottom surface are covered with a lining material 10; a sealing layer 50 is provided on a top surface of the lining material 10 for covering both the side portions of the bottom surface; a buffer material 42 is arranged between the lining materials 10 for covering both the side portions of the bottom surface; a panel plate 43 is arranged on the buffer material 42 and the sealing layer 50; and regions on both the side portions of the bottom surface of the panel plate 43 are fixed to a floor surface via the lining material 10 and the sealing layer 50.