Abstract: Bias tunnel easily caused collapse accident during construction. For Reducing the risk of collapse and the maximum risk loss, the research established the accident tree risk assessment of bias tunnel construction collapse mainly caused by terrain. On the basis of the definition of the risk of bias on tunnel construction, this article studied the basic method of risk assessment using the accident tree Analysis, and built the accident tree chart of bias tunnel construction collapse. This article also made an analysis of the main events causing bias tunnel construction collapse, finally, identified the key events sets. Through the risk loss estimation model by bias tunnel construction, this article estimated loss results and made a real case study at last. The accident tree method provided the effective method for risk assessment of the bias tunnel collapse.this way made risk assessment more accurate.