The invention relates to a power plant environmental-friendly unit input-output calculation method considering the environmental cost, which is characterized in that net present value analysis in a cost-benefit analysis method is applied and comprises the steps of firstly predicting the operating cash flow of each year in an investment project life cycle, then converting various remunerations in the future into a total present value by using a selected discounted present value, and finally carrying out economical evaluation on input-output of a project in the implementation process. The method provided by the invention can solve a problem of input-output comprehensive benefit evaluation before and after the current power plant implements a desulfurization and denitrification project, guides the power plant to reasonably manage project construction planning, and reduces the risk of project engineering construction of the power plant.