In order to strengthen the meticulous management of line loss and improve the economic benefits of electric power company, this paper establishes the model of electric energy loss calculation model of power grid component in HVDC system and diagnosis analysis and loss reduction potential analysis of line loss, develops theoretical calculation and diagnosis analysis system of line loss based on J2EE framework. With the EMS system, SCADA system, production management system, measurement automation system, marketing management system, distribution network automation system, and the data centralized management system, through the open design, it not only realizes the automatic extraction of line loss data and efficient synthesis, but also achieves the line loss theoretical calculation online, energy loss diagnosis analysis and loss reduction potential analysis function. The proposed system has high security and portability, and can provide a scientific decision-making tool for theoretical calculation of line loss and meticulous management, economic operation, power grid planning and energy saving reconstruction, so it has broad application prospect.