This paper aims to investigate the transmission mechanism through which trade policy uncertainty (TPU) impacts bank risk-taking via firms’ capital market performance. The research reveals that TPU significantly affects firms’ capital market performance, leading to reduced stock liquidity, increased stock price crash risk, decreased stock price synchronicity, and lower stock returns. These effects are transmitted to bank risk-taking, resulting in an overall increase in banks’ passive risk-taking and a decrease in their willingness to undertake active risk-taking. Furthermore, we discover that the impact of TPU on bank risk-taking varies across different categories of firms, revealing heterogeneity in this transmission process. This study uncovers the critical mechanism through which TPU propagates in financial markets, offering important theoretical insights and policy implications for understanding and managing financial risk.