The utility model discloses a reducing slip of an insulated tubing string of a thermal production well. The reducing slip comprises a left slip and a right slip, wherein an inner arc segment, a middle-upper arc segment, an outer-upper arc segment, a middle-lower arc segment and an outer-lower arc segment are arranged on the inner wall of the left slip, the radius of the outer-upper arc segment is larger than the radius of the middle-upper arc segment, the radius of the middle-upper arc segment is larger than the radius of the inner arc segment, the circle centers of the inner arc segment, the middle-upper arc segment and the outer-upper arc segment are all arranged on a horizontal shaft, the middle-upper arc segment and the middle-lower arc segment are arranged in a mirror image mode relative to the horizontal shaft, the radii of the middle-upper arc segment and the middle-lower arc segment are equal, the circle centers of the middle-upper arc segment and the middle-lower arc segment are coincided, the outer-upper arc segment and the outer-lower arc segment are arranged in the mirror image mode relative to the horizontal shaft, the diameters of the outer-upper arc segment and the outer-lower arc segment are equal, and the circle centers of the outer-upper arc segment and the outer-lower arc segment are coincided. The structure of the left slip and the right slip are the same, the left slip and the right slip are arranged in the mirror image mode relative to a vertical shaft, the slip is not required to be replaced when oil pipes with three diameters of phi 73, phi 89 and phi 114 are removed, and three kinds of oil pipes can be removed through a pipe clamper. The problems in the prior art are solved, the labor intensity of workers is reduced, and the work efficiency is improved.