Abstract: To investigate the influencing factors of effective stress parameters for shear strength of unsaturated soils and to quantitatively examine their rationality, this study systematically analyzedate of 264 suction-controlled triaxial shear tests and 102 direct shear tests on unsaturated soils from both domestic and international sources. This research focuses on magnitude and influencing factors of effective stress parameters within the commonly encountered suction range (0-1500 kPa), and conducts quantitative examination and clear assessment of four types of effective stress parameters. The key findings are as follows: (1) Within the suction range of 25-400 kPa, more than 26.5% of triaxial test results show effective stress parameter values exceed the theoretical upper limit of 1, especially a maximum measured value of 2.63, breaking through its maximum limit of 1, which is not accidental. The reason is that the effective stress method simply attributes the influence of suction on the shear strength of unsaturated soil to friction and ignores the influence on cohesion; (2) In the suction range of 25-450 kPa, over 15.5% of triaxial tests and over 23.5% of direct shear tests yield effective stress parameter values within the range of 0 to 0.35, which is far lower than 1. The mechanism is related to the increase of the structural development of and internal friction angle of the undisturbed soil with the increase of suction. It shows that low suction does not necessarily correspond to high effective stress parameter values, which is also not a random occurrence; (3) Using a relative error threshold of ±10% as the accuracy criterion, there is a significant deviation of four effective stress parameters, i.e., saturation degree at failure, effective saturation degree at failure, and two published empirical equations including the equation suggested by Khalili, from the experimental values, with qualification rates below 20%. It is found that these four effective stress parameters severely overestimate or underestimate the contribution of suction to the shear strength of unsaturated soils, which seem unsuitable as effective stress parameters; (4) The effective stress parameter on shear strength depends complexly on soil type, suction magnitude, net confining pressure (or vertical net stress), and stress path, reflecting soil viscoplasticity hardening, dilatation and structural properties. Due to the absence of clear patterns, direct measurement of effective stress parameters via suction-controlled triaxial drained shear or direct shear tests remains the feasible method currently.