Aiming at the ambiguity of the evaluation results in the evaluation of the investment benefits of transmission projects and the subjective errors in the weighting of evaluation indicators, this paper proposes a method for evaluating the investment benefits of transmission grid projects based on the improved matterelement extension model. Firstly, a grid project investment benefit evaluation index system is constructed under consideration of the improvement of the power grid by the project being put into operation. A graph model index weighting method based on the principle of graph theory is also proposed to reduce the subjective error of the traditional subjective weighting method. Secondly, the matter element extension model for investment evaluation of transmission projects is established. Finally, 220 kV transmission projects put into operation in a certain area is taken as example for empirical analysis. The investment benefit rating and influencing factors of the projects put into production are studied to verify the scientific practicability of the model.