The invention relates to a method for automatically metering theoretical power loss electric quantity based on database nesting triggers and belongs to the technical field of power grid network loss analysis in an electric power system, energy saving and emission reduction. The method comprises the steps that firstly, data tables of power loss electric quantity values in a unit period and power loss electric quantity metering values in different time periods are respectively established and stored and the triggers are respectively defined on the databases; secondly, the power loss value in the unit time period is written in the data table in real time by online theoretical power loss calculating software, a daily metering value table is automatically updated through the trigger of the power loss electric quantity data table in the unit period, a monthly metering value table is automatically updated through the trigger of the daily metering value table, and a yearly metering value table is automatically updated through the trigger of the monthly metering value table. The method for automatically metering the theoretical power loss electric quantity based on the database nesting triggers improves the automatic degree of online power loss analysis, the change condition of the current daily, monthly and yearly power loss electric quantity metering values can be known in real time, so that circuits, transformers and the like with high power loss are found in time, a scientific method with low power loss is made, and the energy using rate is improved.