In order to explore the critical slope rate of soil and strongly weathered rock slope without damage and the method of deriving the slope safety factor, based on the stratum parameters of Jinan, the critical slope rate of strongly weathered rock without damage was analyzed by using plaxis3d, which can provide reference for the corresponding engineering; for the circular plane sliding mode of soil and strongly weathered rock slope without damage, plaxis3d and MATLAB software were used to analyse the stress field of the slope. The critical slip curve of the slope was obtained by using the slip line field method, and then the analytical solution of the slope stability coefficient was derived by using the Swedish slice method. The results show that whether the rock mass of the soil and strongly weathered rock dual slope is damaged or not is related to the slope height, soil rock thickness and its proportion. When the rock thickness is more than half of the slope height or the slope ratio is greater than 1:0.5, the rock mass will be damaged. Compared with the specific case, the analytical solution shows that the safety factor is smaller, which is beneficial to the engineering safety. For the soil and strongly weathered rock slope, the slope failure can be determined according to the research conclusions of this paper Then the supporting scheme is designed.