The present invention relates to a power transmission and transformation project environmental benefit calculation method and calculation system. The method is characterized by including the following steps that: the evaluation index of the ecological environment is built, and the environmental benefits of the evaluation index in the ecological environment are calculated, wherein the evaluation index of the ecological environment is a green coverage rate; the evaluation indexes of the living environment are built, and the environmental benefits of the evaluation indexes in the living environment are calculated, wherein the evaluation indexes of the living environment include regional noises, electromagnetic influences, fixed waste pollutions, radio interferences and emission reduction measures; an environment construction evaluation index is built, and the environmental benefits of the environment construction evaluation index are obtained; and the environmental benefits of a whole power transmission and transformation project are equal to the sum of the environmental benefits of the evaluation index of the ecological environment, the environmental benefits of the evaluation indexes of the living environment and the environmental benefits of the environment construction evaluation index. With the calculation method and calculation system of the invention adopted, systematic analysis and summarization are performed on a whole process from the project approval decision making, design, construction and completion acceptance to protection and operation of the power transmission and transformation project, the environmental benefits generated by the power transmission and transformation project are evaluated scientifically, and guidance can be provided for the decision making and implementation of projects in the future.