Slope instability is a complex problem in road and bridge  engineering, hydraulic engineering,and construction engineering. The mechanism of slope instability has long been an important content of geotechnical engineering research. Nonetheless, among various slope stability analysis methods, traditional limit equilibrium method is complicated, nonobjective, and cannot provide the only safety coefficient ； while the convenient and practical strength reduction method can not reflect the mechanism of slope instability. In this paper, a simple and intuitive slope-angle-increasing method which reflects the slope instability mechanism is proposed. This method is based on the principle of geotechnical centrifuge and limit equilibrium and is demonstrated by example calculation. The method is to increase the slope angle gradually so that the sliding force is increased and the anti-sliding force is reduced until the slope instability reaches its limit and slope failure happens. In this way, the correlation between slope angle and safety factor can be deduced. The method is demonstrated by example calculation and the result is compared with that of traditional limit equilibrium method and finite element strength reduction method. The comparisons show that slope-angle-increasing method can be applied to slope projects of low groundwater level ， and offers a new research idea for slope stability analysis.