To address the instability problem of shallow-buried tunnel with unsymmetrical pressure under blasting, the potential energy equation of surrounding rock was derived by considering both blasting damage and water weakening effect. Using the cusp catastrophe theory and its calculation method, a catastrophe instability criterion of surrounding rock mass in a shallow-buried tunnel with unsymmetrical pressure under blasting was established. Then, the effects of water weakening, blasting damage and unsymmetrical pressure on the instability of the surrounding rock mass were discussed. Taking Dayangan tunnel in the national high-speed G5615 (Tianbao-Malipo section) as an example, a catastrophe criterion k of surrounding rock mass under different working conditions was calculated according to the physical and mechanical parameters of surrounding rock and the results of the field acoustic wave test. Meanwhile, a shallow-buried tunnel's surrounding rock stability state with unsymmetrical pressure was determined. The results show that the necessary condition for abrupt instability in shallow-buried tunnels with biased pressure under blasting is the abrupt failure criterion k<1, indicating a potential state of abrupt instability. The degree of bias pressure is the critical internal factor affecting tunnel instability surrounding rock mass. Additionally, the greater the degree of bias pressure, the more prone the tunnel is to sudden instability. The practical evaluation results are consistent with the field observations, verifying the practicability and validity of the criterion.