Abstract: In the process of reinforcing construction of long-span masonry arch bridge,usually in some steps main arch of bridge had insufficient bearing capacity due to badly-distributed inner forces,etc. To solve this problem,the authors presented the method of arranging temporary supplement loads on proper position of bridge to balance the structure. Firstly,based on the detailed analyzing relation between ultimate bearing capacity of masonry arch bridge and eccentricity of resultant forces on an arch section,eccentricity was chosen as critical parameter and used to determine whether the section had sufficient capacity without complete calculation. Then, design method of arranging balance weight during reinforcing construction of masonry arch bridge was proposed,and this method was to limit the divergence between eccentricity of resultant forces on section in certain construction step and its boundary e₀by properly distributing supplement load. In order to validate the above method,a 2-span concrete arch bridge with 100 m span length was introduced and its plans of balance weight for 3 construction steps were discussed.