The contribution of surface load to the stability of loess slope should be properly evaluated in order to meet the engineering demand in loess area. It is essential to analyze the stability of loess soil slope by means of the strength reduction finite element method instead of the slices method commonly used in practice so far. Firstly, some researches on stability of loess slope are reviewed. Then some different cases of the mechanism and mode of instability of a loess slope due to surface load are analyzed in this paper. Numerical results not only indicate that the safety factor of loess slope tends to change with the different distribution of the surface load, but also reveal that the distribution of surface load has important effect on the mode of instability of slope.