The present invention discloses an annual cost accounting method under power network system overall lifecycle management. The method comprises: the step 1, establishing a system-level annual cost calculation model; the step 2: calculating the average investment cost of the system-level asset by year; the step 3: calculating the system-level year operation cost; the step 4: calculating the system-level year repairing and maintenance cost; the step 5: calculating the system-level year fault cost; and the step 6: calculating the system-level retirement treatment cost. The problems are solved that the system-level device cost calculation depends on the manual form filling and manual cost accounting and the initial cost, the line loss and the fault cost of the system-level system are not subjected to the statistics to cause the system-level cost accounting error is big and the workload is big and not comprehensive and finally result in big power network system-level planning integrated economy assessment error in the prior art.