The embodiment of the invention provides a circular seam internal supporting device of a storage tank cylinder section to solve the problem that in the prior art, the coaxiality and the circular degree of the cylinder section circular seam formed by a circular seam internal supporting device of a storage tank cylinder section are low. The circular seam internal supporting device is simple in structure and low in manufacturing cost. The circular seam internal supporting device of the storage tank cylinder section comprises a plurality of supporting mechanisms (1), a metal framework (3), a plurality of linear guide rails (4) and at least one joint ring (5). The linear guide rails (4) are axially arranged on the outer side face of the metal framework (3), and the joint rings (5) are arranged on the outer side face of the metal framework (3) in a sleeving mode and can axially move along the linear guide rails (4); the supporting mechanisms (1) are arranged in the circumferential direction of the joint rings (5), and the supporting mechanisms (1) provide radial supporting force outwards from the centers of the joint rings (5).