Abstract: The critical filling height of embankment is a key problem in highway engineering. When the filling height of embankment is less than the critical height, the settlement and stability of a foundation can be controlled. Taking into the consideration of both the effect of σ₂ , intermediate principal stress and the realistic coefficient of lateral earth pressure (K₀≠1), new formulas of the critical edge pressure and critical loading of a foundation are deduced, based on the Flamant formula of a polar coordinate system and unified strength theory. A calculation method of the critical filling height of embankment is also proposed. According to a practical example, a comparative analysis has been made on the calculation results of the critical loading and the filling height of embankment considering different values of b, the coefficient of intermediate principal stress and K₀ , and the coefficient of lateral earth pressure. It can be concluded that this method can reflect the essential of foundation bearing capacity more accurately and be conducive to make the full use of the strength of foundation soil.