The invention provides a GIS (geographic information system)-based three-dimensional power transmission line corridor design method which includes the steps of (1), creating a line engineering drawing; (2), erecting towers in the line engineering drawing; (3), hanging insulator strings; (4), hanging lines; and (5), hanging spacers and dampers. By the method, the problem about after-effect in ranking optimization is solved, the requirement for eliminating the after-effect in dynamic planning is met, and a ranking result is optimized. During ranking of power transmission lines, the problem about the n-variable is changed into the problem of solving n single variables by the method for achieving optimization, thus calculation quantity is small, and optimization is achieved by dividing all the factors into multiple stages and multiple steps. The precision of the calculation result is improved greatly since the calculation quantity is reduced geometrically. Therefore, the method has great significance in reducing construction cost of engineering and improving design quality during power transmission line design.