Abstract: Critical suction is a crucial controlling factor for the penetration of bucket foundations into sand. Most of the existing methods predict the critical suction based on pure seepage numerical analysis, but they cannot reflect the changes in soil permeability coefficients inside and outside the bucket during foundation installation process, also lack of actual data to rerify the theortetical method.A series of model tests were conducted on the suction of the bucket foundation in sand, including testing the suction process during foundation penetration and obtaining the permeability coefficient ratio change law through reverse analysis. The results show that when the soil in the bucket Produces piping phenomenon, the negative pressure in the bucket is instantly reduced. As immersion depth increases, so does the critical suction value. Additionally, the ratio of permeability coefficients between soil inside and outside of the bucket increases as a power function. Assuming that soil permeability coefficient remains constant during penetration, prediction results for critical suction are obtained. According to the test results, the calculation formula of critical suction during bucket foundation penetration in sand is improved and an engineering case study is conducted.