There may be serious static security problem after UHVDC related single or multiple DC locking faults, on-line analysis is necessary. At present, on-line simulation computational speed of the security&stability control is difficult to meet analysis requirements and the results of DC reactive power control strategies are not accurate. An On-line static security analysis method of UHVDC faults is proposed, considering the security&stability control strategies and primary frequency regulation characteristics. A quasi-static simulation method is used to estimate the change of active injection of each node under the faults, according to time sequence of security&stability control first action and primary frequency regulation second action. In the simulation, the DC reactive power control function model is established by the bus type conversion of the converter station,thus the accuracy and convergence of the calculation is improved. The effectiveness of proposed method is verified by actual cases.