Abstract: The extreme conditions of a yield function,which was used as one of the fundamental equations for ultimate analysis of soil mass,together with the equilibrium equation and yield conditions,constituted a complete limit equilibrium problem(a problem of boundary conditions of a load).The velocity field and the velocity equation of the slip surface family may be used to establish a new ultimate analysis method-Generalized Limit Equilibrium Method.An approximate formula for calculating the ultimate load on a foundation was derived by using the generalized limit equilibrium method.The extremum theorem of an ultimate load and the results of calculation proved that if the chosen slip surface(family) came near to the genuine slip surface,the obtained approximate value of an ultimate load was more close to the genuine solution.