Abstract: Light non-aqueous phase liquid (LNAPL) contamination poses persistent challenges in groundwater systems, particularly under complex hydrodynamic conditions. However, the coupled dynamics between LNAPL migration and groundwater-level fluctuations, as well as resistivity response characteristics, remain insufficiently understood. This study investigated LNAPL migration behavior and associated resistivity responses under three representative hydrogeological conditions: unsaturated media, constant groundwater level, and fluctuating groundwater levels. Laboratory sandbox experiments were conducted using acrylic tanks filled with fine sand, with No. 0 diesel serving as a representative LNAPL. High-density electrical resistivity tomography (ERT) was employed to monitor LNAPL migration, and time-lapse inversion was performed using ResIPy software to quantify spatiotemporal resistivity variations. Under unsaturated conditions, LNAPL migrated primarily in the vertical direction, with a maximum migration rate of 5.2 cm/h. After migration stabilized, the maximum changes in resistivity between the top and bottom of the medium were 317.84% and 430.35%, respectively. Under constant groundwater levels, LNAPL accumulated at the oil-water interface to form a floating oil slick due to its lower density than water, with a maximum migration rate of 1.1 cm/h. After stabilization, the maximum changes in resistivity at the top and bottom of the medium were 285.42% and 451.54%, respectively. Fluctuations in the groundwater level promoted the lateral diffusion of LNAPL while altering the thickness of the oil layer and the morphological characteristics of the high-resistance lens. Water level fluctuations influenced LNAPL migration by altering the medium’s moisture content and buoyancy effects, while the accumulation of LNAPL altered the liquid phase pressure within the sand box, thereby affecting the groundwater level. The findings of this study provide valuable guidance for the precise investigation and development of remediation plans for sites contaminated with light non-aqueous phase liquids (LNAPLs).