Abstract: Structural failure modes play an important role in the seismic performance of RC buildings under strong earthquakes. Typical failure mode-based failure probability of the RC frame supported by foundations with different elevations is evaluated by cut-set method based on system reliability theory, and compared with that of regular frame counterparts. The results show that the annual average failure probability of ultimate shear mode of the frame supported by stepped foundation is higher than that of regular frames, and the risk of shear failure before bending failure exists. Appropriate strengthening measures should be conducted to satisfy the design principle of strong shear-weak bending. By comparing the designs with different shear-amplification coefficients, it is suggested that the seismic level which determines the shear-amplification coefficient be one level higher for the design of shear bearing capacity of the upper embedding column, and dense hoop reinforcement be arranged over the whole length of the upper embedding column.