The invention discloses a method and system for regulating the balance weight of a rotation structure in the construction process of a bridge horizontal rotation method. When a beam body is formally rotated, the eccentric bending moment subjected by the beam body is directly calculated through relevant parameters of the reading changes of a dialgauge, the jacking force of lifting jacks and the like before and after support dismantling is conducted on the beam body to further obtain balance weight loading. The structure of a rotated body is considered as steel concrete but not a pure rigid bodystructure, the regulation accuracy of the balance weight can reach 1kg, and the safety of rotation is greatly improved; the method is simple in testing principal and higher in accuracy, and comparedwith a regular testing method, the construction cost is greatly reduced to ensure the stability, safety and reliability of the bridge rotation construction.