Abstract: In order to study the size effect, a model experiment on the electro-osmosis combined with loading is designed and conducted. Through the comparison among model experiment on electro-osmosis combined with loading, model experiment on simple electro-osmosis and in-situ experiment on electro-osmosis, it is demonstrated that the large difference of cracks is the main reason why the model experiment on simple electro-osmosis draws an opposite conclusion with the in-situ experiment. The size effect caused by geometric boundary can be eliminated by reasonable loading, which makes the cracks similar to those in the in-situ experiment, so the model experiment on electro-osmosis combined with loading can better simulate the in-situ experiment. As the size effect is eliminated, the main factor influencing the electro-osmosis dewatering is the effective electric field rather than the current density. Among hexagonal, rectangular, and parallel and transposition configurations, the hexagonal configuration which has the maximum area of effective electric field is the most effective and economical, so it is recommended to be employed for electro-osmotic treatment.