Abstract: In order to improve stability of foundation pits against the basal heave failure,a new method called critical width method(CWM)for calculating the factor of safety against basal heave failure was suggested according to Terzaghi’s theory of bearing capacity of foundation and considering that only a single-sided sliding surface existed in real cases of failure.The concept of critical width corresponding to the minimum factor of safety was suggested and the theoretical solution of critical width was given for cases of homogeneous soil foundations.Parametric analyses were conducted to comprehensively understand the problem of basal heave failure of foundation pits.The allowable value of the factor of safety for the new method was also suggested.The validity and significance of the critical width method were then demonstrated through comparative analyses of practical cases.