Aimed at the problem of difficult to assess the stability of quadruped robot for weeding walking on irregular farmland surface, a triangular pyramid method was proposed based on the force-angle stability measurement. According to the relationship of angle point tip-over angle and axis line tip-over angle, the stability judging criterion of minimum stability angle was obtained. Tilting performance coefficient was used to evaluate the robot’s static and dynamic stability synthetically. The effects of ground tilt angle, external load and external torque of irregular farmland surface on the robot’s stability were discussed by numerical simulation. The prototype robot with size of 170 mm×130 mm×140 mm was used to test the minimum stability on 0°–45° irregular corn land, which was driven by servo and had 8 freedom degree The results showed that external load, ground tilt angle have a significantly influence on the stability, and the ground tilt angle was linearly dependent on the stability. Compared to the results of numerical simulation, the average relative error of minimum stability angle was 9.46% and correlation coefficient of 0.979 6.