Understanding the transport behavior of a gel system in porous media is of great significance in enhancing oil recovery (EOR) for high water cut oil reservoirs. However, the length of the experiment models (sandpack or core sample) in current studies is usually in the range of centimeter scale, which is too short to track the full movement path of gel particles. In this work, 10-m long slim sandpacks were adopted to conduct gel flooding experiments. The pressure and polymer concentration distribution along the sandpack was tracked, and scanning electron microscope (SEM) technique was employed to observe the pore morphology after the gel flooding. The results show that the movement of polymer particles is usually within 7m away from the inlet due to the adsorption and retention in the porous medium. For 0.4 PV injection cases, SEM images show that the pore morphology at the inlet region exhibits a stable polymer network, while the network structure disappears at the outlet, along with the decrease of fluid viscosity from 620.1mPa·s to 1.2mPa·s. However, we can still find the stringy state polymer after 5m movement and the viscosity is 584.0mPa·s for 1 PV gel injection cases. Four characterization parameters, including equivalent viscosity, breakthrough pressure gradient, dimensionless gelation gradient, and plugging ratio, were proposed to quantitatively characterize the performance of gel flooding. In addition, empirical models were also obtained to predict the four parameters through multi-parameters fitting, and these models facilitate the characterization of the gel flooding performance. This is the first work, to the best of the authors’ knowledge, using long slim sandpack (10m) to experimentally study gel system transport in porous media, which provides theoretical implications in enhancing oil recovery.