On-line voltage stability assessment（VSA） of power system based on load margin computation has been a basic module in modern EMS. However， the static load voltage characteristics， OLTC， switchable shunt capacitor， under-voltage load shedding are not considered in most VSA tools. Furthermore， the thermal limit violation induced branch outage is not considered either. Therefore， the maximal power limits obtained in VSA are not of practical significance， and not meet the security alarming and preventive control requirement. A novel on-line static VSA method based on continuation power flow technique is proposed. The effects of load voltage characteristics， automatic devices and relays of transmission lines are considered. The proposed method has been tested on a practical system in China. The numerical results show that the proposed method is more suitable for on-line voltage stability assessment.