Assessing the operational risk of a regional power grid objectively and quantitatively can help effectively locate the weakness of the power grid，which is of great practical significance for the operation and maintenance of the grid. From the point of view of load loss due to node voltage-loss and branch overload， an operational risk index system is defined. By taking into full account the impact of various factors on the operational risk， such as the action of protection， busbar automatic transfer switch， and dispatchers' load-shedding， a novel operational risk assessment of regional power grid considering the developing process is presented. The numerical results of Shenzhen grid typical operation mode demonstrate the practicability and maneuverability of the approach proposed.