Stability analyses of lateral slide and soft foundation extrusion are required only in codes about application of geosynthetics The practical location of vertical boundaries of sliding body always doesn’t coincide with that postulated by present methods for stability analysis of lateral slide and soft foundation extrusion and the influence of spread of superimposed stress can’t be taken into account by present methods. It is proposed that location of vertical boundaries of sliding body isn’t limited at shoulder or toe of fill and the superimposed stress is calculated by Flamant solution to overcome shortcomings of present methods. It is shown by analysis that stability analyses for circular slide, lateral slide and soft foundation extrusion should all be carried out for fill on soft foundation, vertical boundaries of sliding body with minimum safety factor of stability aren′t often at shoulder and toe of fill and the safety factors of stability calculated by the proposed method are often different from those calculated by present methods.