Abstract: This paper analyzes the variation law of the Mohr's stress circle for normally consolidated soils in direct shear tests and triaxial compression tests. By comparing and analyzing the stress paths during the shearing process of the two tests, it is found that the directions of the stress paths are different between the direct shear test and the triaxial compression test. Two non-parallel straight lines in the same plane must intersect at a point, which simultaneously represents the vertex of the failure Mohr's circle for both the direct shear test and the triaxial compression test. Based on the analysis, two major principal stresses corresponding to the consolidated Mohr's circles of the soil sample before the start of the direct shear test and triaxial compression test are obtained, namely the direct shear initial stress and the triaxial initial stress. According to the condition that the stress states are equal at the intersection point, a relational equation between the two initial stresses is established; furthermore, through analysis, the conversion method between the coordinate systems of the direct shear test and the triaxial compression test is derived, and a linear equation with normal stress as the variable is obtained. When any value is substituted for the normal stress variable in this linear equation, the equation holds true, so it can be determined that both coefficients of the equation are zero, thereby deriving the mutual conversion formulas between the direct shear parameters and the triaxial compression parameters. The experimental results show that the theoretical values are basically consistent with the measured data, verifying the reliability of the proposed theoretical relationship.