Abstract: The strength of sublayer of the two-layer foundation which is a soft clay covered by thin crust often can't satisfies the requirements of building code. This paper uses the limit equilibruim theory to calculate bearing capacity of two-layer foundation. By the mechanical parameter φ of soil, we can get the approximate shifting nets. Then we get the bearing capacity p1 due to the cohesion cand the bearing capacity p2 due to the weight of soil respectively. Finally, the ultimate bearing capacity can be calculated by pu = p1 + p2. We can determine the allowable bearing capacity p2 with enough reliability and take some appropriate measures in design, This method is economic and safety in practice.