The on-line dynamic security assessment system based on intelligent scheduling system calculates and analyses power system using real time on-line data,achieves a leap from the off-line analysis to the on-line analysis of the power grid.The main structure,function and calculation process of the dynamic security assessment system of Jiangsu power grid are briefly introduced in this paper,using the safety and stability analysis of Jiangsu power grid encountering tornado and hail disaster in June 23,2016 and after a substation bus fault in November 4,2016 as calculation examples,the results show that the dynamic security assessment system can calculate and analyze the power grid,and give the corresponding auxiliary decision-making measures timely and effectively,enhancing the emergency handling capacity of power dispatchers in emergency situations,and plays an important role in ensuring the safe and stable operation of the power grid.