The strength reduction finite element method was used to analyze the stability of the typical section of the South Main Canal of South to North Water Diversion Project. The Duncan-Chang nonlinear constitutive model was employed to describe the stress and strain relationship of the soils. The displacement mutation of the maximal horizontal displacement of the slope was used as a criterion for evaluating the instability. The research results based on the FEM reduction stability analysis was verified by traditional simplified Bishop Method. There is good accordance between both methods, which proved that the analysis is reasonable. And both results fulfil the designation requirement.