Abstract
The subprime mortgage crisis of America has increased the importance of the banking system security, and the subprime mortgage crisis in the banking sector's performance is constantly being infected by a bank's bankrupt, and ultimately makes contagion. In this article, firstly, according to the idea of maximum entropy estimates the payment transactions matrix and then presenting a risk of spreading mechanism of the specific process, finally take the Finnish inter-bank payment system for example do a risk analysis of infection.