Abstract: In view of the general problems of error tendency for studying the earth pressure on retaining wall, by clarifying the basic mechanical conceptions of soil arch and soil arching in soils of retaining wall, it is analyzed that the change laws of earth pressure coefficient based on the principal stress trajectory with the frictional angle between wall and backfill are contrary to those of the classical Coulomb’s. The larger the difference between them is, the larger the effect of the horizontal earth pressure distribution. The existence of this difference is just the soil arching considered by the principal stress soil arch method, and it is the largest falsehood. According to the math ematical principle analysis of horizontal earth pressure distribution formula derived by differential stratum, it is expounded that any theoretical method to use the differential stratum to obtain the result that the earth pressure is curve distribution is necessarily false, that is to say they are contrary to the classical theories, and the earth pressure coefficients behind retaining wall are self-contradictory.