Abstract: After the reform of transmission and distribution price, the demand for lean management of power grid companies is increasing. The cost of a project has direct impact on investment decisions, so the traditional rugged cost calculation method cannot meet the current demands. To this end, a cost accounting method is proposed. In this method, according to the efficiency idea, the operation and maintenance cost of project is allocated and calculated. Firstly, the Elastic Net algorithm is used to screen the factors affecting the operation and maintenance cost to determine the performance standards of key factors. Secondly, the criteria importance though intercrieria correlation（CRITIC） method is used to measure and calculate the weight. The cost allocation coefficient of a single project is obtained, and then the allocated cost of the project is calculated to realize the accurate measurement of the operation and maintenance cost of the project. Finally, the typical project data of a province in China is selected to verify the proposed model.The results show that the proposed model can more accurately calculate the operation and maintenance cost of the power grid project.