Abstract: The suction caisson serves as an important anchoring foundation for floating platforms, widely used in deep-sea oil/gas platforms and offshore wind turbines due to its convenient construction, cost-effectiveness, and structural reliability. This study, based on the scaled model tests conducted in saturated sand under displacement control, investigates the uplift bearing capacity, ultimate failure modes, and pore pressure evolution pattern of suction caissons under varying loading rates and aspect ratios. The results indicate that: (1) Under fully drained conditions, the main uplift resistance of the suction caisson is derived from structural self-weight and sidewall friction, with negligible contributions from internal negative excess pore pressure and minimal loading rate effects on the bearing capacity; (2) Under partially drained conditions, the uplift bearing capacity increases correspondingly with the growth of negative pressure, demonstrating significant influence of negative pressure on load-bearing performance; (3) Within a certain range, as the aspect ratio increases, the dissipation rate of pore pressure decreases while the sidewall friction resistance enhances, leading to substantial improvement in ultimate uplift capacity.