Abstract: The calculation error of additional effective stress induced by foundation loadings; based on different grouping and various solutions for one problem; are discussed in this paper. It is found that the error tolerances for parameters K_o 和4K_c are between 0.005 and 0.007. This paper further discusses the complementary relationships between K_c和4K_c and the related calculation formulas. These relationships are the basis of understanding the calculation errors.