The two limit equilibrium methods of bulk material (Variation method and wedge model method) is employed to analyze models of sliding cuneiform volume of bulk solid, the lateral pressure formula for squat silos and equations of failure plane about sliding cuneiform volume are obtained. Variations of the positions of failure plane with height/diameter ratio are analized on the basis of the analysis for positions of failure plane by solution of these equation. The applied range and calculation method of the formula, and pressure distribution are discussed. The effects of friction between bulk solid and squat silos on the positions of failure plane and lateral pressure of bulk solid are discussed. The conclusion is that caculation results is available for squat silo design when the friction takes no into account, and the applied range of the formula is that height/diameter ratio equals 1.3. It is widely appicable for almost all squat silos. The caculation results agree with that of the full-sized silo experiment. This is a reasonable calculation method for design of squat silo.