The invention provides a reducing spanner and relates to a spanner. An inner hexagon ring (1) is arranged at one end of a handle (10). Threads (4) are arranged on the two sides of the portion from the middle to one end of the handle respectively. A sliding groove (9) is formed in the portion from the middle to an inner hexagon opening (2) of the inner hexagon ring at one end of the handle. The lower portion of a sliding block (13) is clamped into the sliding groove. An inner thread (17) of a rotating ring (7) is connected with the threads of the handle. A baffle (5) arranged in the middle of the sliding block is located on one side face of a V-shaped ejector rod (3) of the rotating ring. A square locking rod (12) is arranged on the portion, close to the rotating ring, of the other end of the sliding block. The baffle and the square locking rod clamp the front side face and the rear side face of the rotating ring. The V-shaped ejector rod is arranged at the end, where the inner hexagon ring is located, of the sliding block. As the rotating ring is arranged on the portion, away from the inner hexagon ring, of the handle, a clamping opening can be accurately adjusted once when clamped on the nuts or the bolts, and operation progress is effectively accelerated.