Abstract: After the Yunnan power grid of China and the China southern main power grid are interconnected asynchronously, the large amount of surplus power caused by the fault of sending DC lines makes the problem of system frequency stability more severe. Aiming at the DC blocking faults, the contribution factor of each generator unit to the surplus power caused by the fault is derived, and a tripping priority index with fault severity and probability taken into account is proposed. Furthermore, the configuration principles of the first-round and the last-round frequency settings for over-frequency generator tripping are discussed,and the dynamic cross-sequencing method is leveraged to meet the dispersion requirements of the tripped units. In order to improve the simulation efficiency, the approximate solution of over-frequency generator tripping is estimated by adjusting power first, and then the solution is modified by using the steady-state frequency constraint to complete the optimal configuration of the tripped units at each round. Finally, the generated typical faults are verified by using the clustering method. The simulation results demonstrate that the proposed method not only increases the minimum frequency but also reduces the maximum frequency during the transient process, which is more beneficial to the system stability and avoids the risk of under-frequency load shedding. At the same time,the overall tripping capacity is effectively reduced on the premise of ensuring that the steady state frequency is within the allowable range.