Abstract: In sandy soils, there exists a special drainage condition where pore water is neither fully drained nor completely undrained, characterized by partial drainage of pore water. To investigate this phenomenon, this study first established a numerical model for biaxial compression simulations using the Discrete Element Method (DEM) approach. Subsequently, a mechanical model that can achieve different drainage conditions was developed by varying the displacement rates of servo walls. The mechanical behavior of sandy soil under these drainage conditions was systematically investigated. The simulation results are as follows: (1) Drainage conditions have a significant effect on the mechanical behavior of particles, with the increasing of strain increment ratio (H), the stress-strain curve of particles shows a transition from strain softening to strain hardening, and the evolution trend of the super porous water pressure also varies with drainage conditions. These two factors collectively govern the stress path of sands under different drainage conditions. (2) Under different drainage conditions, the mechanical coordination number (MCN) and the average contact force (F) between sandy soil particles showed significant differences, i.e., the higher the strain increment ratio H, the larger the MCN and F of the samples. Our results provide new insights into the mechanical properties of sands under complex drainage conditions, which are of great significance forstability analysis and engineering design involving sandy soils in practical applications.