The utility model relates to a cross-section-variable circular wall formwork erecting structure. The cross-section-variable circular wall formwork erecting structure comprises a circular inner-wall formwork, a circular outer-wall formwork and split bolts, wherein the circular inner-wall formwork and the circular outer-wall formwork are oppositely arranged, and the split bolts are used for fastening the circular inner-wall formwork and the circular outer-wall formwork. The circular outer-wall formwork comprises a first outer formwork body erected at the lower portion and a second outer formwork body erected at the upper portion, the second outer formwork body is close to the circular inner-wall formwork compared with the first outer formwork body, the first outer formwork body is erected on the ground, a supporting rod is arranged at the top end of the first outer formwork body, and the second outer formwork body is erected on the supporting rod. A circular wall is a cross-section-variable wall, an upper wall body is retracted towards the inner side, and therefore the upper portion of the circular outer-wall formwork is free of a supporting foundation; the supporting rod is fixed to the top end of the lower portion of the circular outer-wall formwork, the upper portion of the circular outer-wall formwork is fixedly supported with the supporting rod, the supporting rod is firm in connection, the construction quality is guaranteed, and formwork erecting of the cross-section-variable wall is achieved.