Construction of the west-to-east transmission project is of great significance to the optimal allocation of energy resources and the development of energy-saving and emission reduction of local community within the whole area covered by China Southern Power Grid（CSG）.A structure analysis model of the line loss rate is built，based on which the contribution of the west-to-east transmission project to the comprehensive line loss rate of CSG can be calculated.Using the method of system operation simulation and scenario comparison analysis，an analysis is conducted to quantify the energy-saving and emission reduction benefit brought about by the development of the west-to-east transmission project in CSG over the last decade.Furthermore，a sensitivity analysis between energy-saving and emission reduction benefit of the west-to-east transmission project and its line loss is conducted to reveal its cost-benefit relationship in terms of energy-saving and emission reduction.