The liquefaction phenomenon occurs when the groundwater is pumped up through the top of sediments as the pore pressure increases due to the earthquake. There have been many studies on the loose sandy soils and various samples through repeated triaxial compression tests and shaking table tests, but there have been few studies on the effects of particle size distributions and the fine contents of sand on the liquefaction of sand. In this study, the undrained repeated triaxial compression tests were performed on sands with different particle size distributions, confining pressures, relative densities, and deviatoric stresses. The results of analysis showed that, with increasing relative density, SW(Well-graded sand) samples had higher liquefaction strength than SP(Poor-graded sand) samples. This is due to the lower void ratio of sand in SW samples than in SP samples. It was also found that the liquefaction strength decreased with a high fine content due to he rapid destruction of the filling of fine particles between the soil particles, leading to lower liquefaction strength.