Abstract: Provided are a tank support jig and a tank cleaning method. The tank support jig for supporting a cylindrical tank includes a curved body having a first end and a second end that face with an interval in between; and a connecting member disposed across the interval, the connecting member connecting the first end and the second end of the curved body such that the interval is adjustable, in which the curved body and the connecting member form an annular structure for the tank that is to be placed horizontally inside the annular structure with the curved body in close contact with at least part of an outer circumferential face of the tank along a circumferential direction of the tank.