A large number of road and disaster site surveys have found that unfavorable cracks are widely distributed on the outer surface of the slope, and failure conditions such as seismic load, hydrostatic pressure, and surcharge load will increase the risk of crack slope instability. In order to analyze the safety performance of slope with different kinds of cracks under different failure conditions in detail, this paper established a comprehensive evaluation method for the stability of slope with crack under any depth and location by combining strength reduction method and upper bound limit analysis, and derived the equation of safety factor; To optimize the algorithm, combining the random search method with the non-linear sequential quadratic programming, this method solved a large number of problems such as iteration in the calculation, fall into the local optimal solution; The paper restored the morphology of the slip surface of the slope with crack and compared the location and depth of critical cracks with the finite element calculation software Optum-G2 to verify. The results show that: (1)compared with the classical solution, the optimized algorithm significantly improves the stability and accuracy of the calculation; different failure conditions will have a greater impact on the stability of the slope. (2)Under the same parameter design, deeper and more distant cracks tend to occur under more adverse different failure conditions. Finally, a series of safety charts are drawn using the conclusions of this study, which can be used as an initial assessment of slope safety by engineers.