This paper presents the results of the study on the reinforcement design of a slope in Ho Chi Minh Road, Vietnam. It is pointed out that the best mechanical index for slope design calculation is the data obtained from geological investigation and field investigation inversion. Through the Ho Chi Minh Road slope design study, the author realized that the slope between soil and rock slope using the plane slide model analysis and the circular slide model analysis results are basically the same. Therefore, the author comes to the following understanding: in a sense, the task of slope engineering design is not to carry out accurate calculation, but to carry out correct judgment. In this paper, it is proved that the geological condition is the main internal factor affecting the stability of slope, and the water is the main external factor affecting the stability of slope. Therefore, water treatment and control is a problem that slope reinforcement engineering must solve.