The twenty-first century is an era of rapid development after the integration of blockchain technology and supply chain finance. Blockchain has been widely used in financial risks because of its decentralization and trust. This paper mainly analyzed the risks in finance through blockchain technology, and made reasonable preventive measures against the risks. It focused on the relationship between blockchain technology and financial risk, as well as the application of blockchain technology in the financial field, such as the causes of risk and corresponding prevention strategies. Risk measurement was carried out through the traditional variance method and the financial market value at risk (VaR) method, mainly in the three aspects of security risk, liquidity risk and yield. The result showed that the VaR method based on blockchain technology reduced the risk by 0.2 compared with the traditional risk assessment method. The deviation was small and the volatility risk was low, which could accurately evaluate the financial risks. The final yield was also about 8% higher. This article has important reference significance in the prevention of financial risks through blockchain technology.