The invention relates to a line loss lean comprehensive management system and a line loss lean comprehensive management method. Relevant line loss data dispersed at automation systems are integrated so as to establish a uniform line loss databank and eliminate line loss information isolated island. The data is read on line so as to calculate the line loss, and the conventional line loss calculation is changed into on-line statistics and calculation from afterwards statistics and calculation, so that the real-time property in line loss analysis is enhanced. The line loss situation of an electric power bureau is calculated in the overall angle, the calculation and analysis on the line loss cover all voltage grades of a power grid, and the comprehensiveness and the completeness in line loss calculation and analysis are ensured. By adopting the on-line calculation mode, the situation that in the past the calculation and analysis can only be carried out on typical days is changed, the line loss analysis does not change along with the change of the season and the external environment any longer, the calculation result is more accurate and real, the situation that in the past only the line loss result is singly and roughly analyzed is changed, the working cost is lowered, and the working efficiency is improved.