In the post-epidemic era, commercial banks have promoted their own digital transformation by deepening cooperation with third-party payment institutions, however they also inevitably bring systemic risks. This paper builds a banking network and dual-channel risk contagion model based on the balance sheet data of 201 Chinese banks and discusses the risk contagion of third-party payment institutions to the banking system more comprehensively. The key finding of this paper is that, compared with a single risk, dual-channel risk has an amplification effect of 1+1>2, resulting in excess loss, which is more destructive. When the risks of third-party payment institution channels and interbank channels work together, the contagion of risks in the banking system will show nonlinear changes, causing large excess losses and significantly amplifying the contagious effects of risks.