Aiming at the problem that financial systemic risk is harmful and difficult to measure accurately,a new measurement method is proposed. Based on the tail correlation of stock return calculated by Clayton Copula function,this paper defines systemic risk as the weighted average probability that a crisis in each financial institution causes a crisis in the entire financial system.Empirical analysis chooses 40 listed financial institutions’daily stock logarithmic return data,and divides 40 financial institutions into three subsystems by K-means method: banking,securities and insurance,and measures the systemic risk of each subsystem and the whole financial industry respectively. The results show that ,in recent years,the systemic risk of insurance industry is the highest,followed by banking industry and securities industry is the lowest,but the systemic risk of securities industry fluctuates most dramatically. The systemic risk of the whole financial industry has been in a high and fragile state,which is consistent with the actual situation.