A decision-making support system for a sewer maintenance that includes a graphic user interface that outputs a function selection means of a user and a decision-making support result through a GIS-based graphic screen, a sewage storing unit that stores sewer data including a sewage pipe network data, an aged pipe diagnosis evaluation factor data and a detailed item-based weight data, a sewer maintenance decision-making module that judges a preset object sewer-based aged degree and a sewer exchange priority based on the data stored in the sewage data storing unit and outputs a decision-making support result for the computed sewer maintenance to a user through the graphic user interface, and a sewer maintenance control module that controls the operations of the graphic user interface, the sewage data storing unit and the sewer maintenance decision-making module based on a preset control program.