[Purposes] The angle of rupture of slope is an important parameter for slope stability analysis and reinforcement design, At present, there are some controversies about the method of determining the rupture angle of slope. [Methods] In this paper, the rupture angle of slope is analyzed by three methods, namely, Moore's Coulomb strength theory, slope stability and retaining wall earth pressure calculation. [Findings] It is pointed out that the rupture angle of slope is related to the stability of the slope, and the formula for calculating the angle rupture corresponding to the minimum stability coefficient of an upright slope is deduced. It is shown that the rupture angle obtained by stability calculation is the rupture angle corresponding to the safety factor of the slope, and when the stability factor of the slope is greater than 1.00, it is the potential rupture angle, and when the stability factor of the slope is just equal to 1.00, the rupture angle at this time is the critical angle of rupture. [Conclusions] The rupture angle obtained by using the soil pressure calculation method of the retaining wall is the rupture angle corresponding to the maximum soil pressure, and is not the critical rupture angle of the slope. Technical code for building slope engineering (GB 50330—2013) based on the idea of calculating soil pressure of retaining wall to determine the rupture angle of slope is unreasonable, and it is recommended to modify it.