This paper focuses on providing interpretations for the cause of the contagion risk among Chinese banking and real estate industries． We test the cause of the contagion risk from two perspectives: the debt net_x005fwork and investor behavior．The results indicate that debt connection is the main inducement of contagion risk，but the behavior of investors can also increase the possibility of risk，especially in the situation of severe asymmetric information between investors and companies，even no fundamental changes exist. Based on the results，a series of policies and advices are suggested in this paper to strengthen the inter industry risk of contagion management and regulate the financial market．