The invention relates to a tank chain type leg support extending mechanism. The tank chain type leg support extending mechanism comprises a main body structure, an extending structure and a coating structure, wherein the main body structure comprises a foundation mechanism, a fixed bracket and a driving mechanism, wherein the fixed bracket and the driving mechanism are mounted and fixed on the foundation mechanism; the extending structure comprises an extending bracket, a track mechanism and a tank chain assembly, wherein the extending bracket is connected with the driving mechanism and is fixedly connected to the fixed bracket in a slidable manner; the track mechanisms are mounted and fixed on the two sides of the extending bracket; the tank chain assembly is mounted and fixed on the extending bracket through the track mechanisms; one end of the tank chain assembly is connected with the main body structure; and the coating structure comprises a surface sleeve covering the main body structure and the tank chain assembly, wherein the two ends of the surface sleeve are correspondingly connected with the main body structure and the tank chain assembly. The tank chain type leg supportextending mechanism forms a whole body and has the advantages that the appearance beauty is good, the cleaning is convenient, and clothes of passengers cannot be clamped.