A PRA-based partitioning method for coordinating power-system planning with operation comprises the steps that S1) basic data of the grid is read in, and an accident set is selected; S2) power flow is calculated based on BPA software, whether problems as overload or overvoltage of branches occur is determined, and the static safety analysis is carried out; and at the same time, models of component failure rate and failure event probability are established, and the component failure rate and failure event probability are calculated; S3) based on a sensitivity matrix, load loss caused by a fault event is calculated via a safety correction strategy; S4) according to the fault event probability and the load loss caused by the fault event, the probabilistic rick index of load loss is calculated, and quantitative risk assessment is carried out; S5) according to the accident grade determining criteria and system bearing capability, load loss values allowed by different accident grades of the system are determined, and different accident grades for which planning and operation are respectively responsible are clearly determined; and S6) the responsibility boundary value between planning and operation obtained by S5 is compared with the probabilistic risk index of load loss of the fault event to determine the responsibility area to which the fault event belongs.