Abstract: Aiming at simplifying the application of the Culmann’s graphical construction in fold line slopes , the bio-fold and tri-fold line slopes behind the retaining wall are taken as the analytical models based on Wang Kuihua’s amelioration on straight line slopes. According to the Coulomb’s earth pressure theory and the similarity between the geometric triangle and the force vector triangle, a new graphical method is developed. Compared with the Culmann’s graphical construction, the newly ameliorated approach needn’t calculate the weight of the slide masses, and either needn’t measure the line segments out proportionally to present the weight of the slide masses. The proposed approach needs fewer calculations and is more convenient, and the results are more precise.