Provided is a method for controlling transversal displacement of a high-speed railway long-span arch bridge. The method effectively solves the problem of transversal displacement control of a long-span deck type railway concrete arch bridge, enables the structure design of the long-span deck type railway concrete arch bridge to be simpler and more reasonable and lowers bridge engineering investment effectively. A main bridge structure system is composed of a main arch ring, on-arch pier studs and a main bridge beam part, the main bridge beam part is regarded as an equivalent simply supported beam being free of transversal restraining of the on-arch pier studs, the main arch ring is regarded as an elastic support for the on-arch pier studs, and the main arch ring and the on-arch pier studs only transfer horizontal loads to the equivalent simply supported beam. The on-arch pier studs are arranged on the main arch ring uniformly, horizontal force transferred by the on-arch pier studs is equivalent to horizontal uniformly distributed loads, a transversal displacement curve of the main bridge beam part is fitted by a transversal deflection curve of the equivalent simply supported beam under the effect of the horizontal uniformly distributed loads, the min-span horizontal deflection delta of the main bridge beam part is controlled according to the following formula that delta<=L/3200, the requirement for the transversal smoothness of a high-speed railway line can be met effectively, and in the formula, L is the length of the main bridge beam part.