This chapter focuses on laboratory experiments for measuring the hydraulic parameters of unsaturated soils. These parameters include the soil–water characteristic curve (SWCC) and the permeability coefficient for unsaturated soils, both of which play a critical role in evaluating slope stability during rainfall events. Their importance lies in providing the fundamental input data for seepage and stability analyses. The chapter then presents a one-dimensional seepage test, accompanied by a numerical seepage analysis conducted under identical boundary conditions to validate and interpret the experimental results. It also describes a rainfall-induced slope model test, designed to simulate the coupled hydrological and mechanical responses of slopes under rainfall infiltration. Corresponding numerical simulations are performed to enable a comparative analysis, thereby enhancing the understanding of slope deformation and failure mechanisms. These experimental and numerical investigations offer valuable insights into the hydrological and geotechnical processes that govern slope stability under rainfall conditions.