Abstract: Typical deformation and failure of expansive soils usually occur under conditions of wetting and low confining stress. However, the mechanisms of coupling between mechanical and hydrological behaviors under those conditions are still obscure. Therefore, this paper investigates the soil water retention, volume change, and strength behavior of expansive soil through systematically designed suction-controlled hydro-mechanical coupled testing under varying saturation conditions along wetting path. The experiment program involves with instruments including double-cell unsaturated soil triaxial test system and Fredlund soil water characteristic device. The tests last almost 800 days, and the soil water retention, volume change, and strength behavior of Jingmen medium swelling soil under conditions of wetting and low confining stress are acquired. The Barcelona basic model is used to describe the unsaturated stress-strain-strength behavior under those conditions. The van Genuchten model is used to describe the unsaturated seepage process. Combined with the other testing results of the soil over the past 10 years, the complete 13 BBM parameters and VG model parameters of Jingmen medium swelling soil under those conditions are calibrated. The constitutive modelling shows that above models and parameters can reproduce the mechanical behavior of the soil under conditions of wetting and low confining stress effectively. The aim of this paper is to improve the prediction capability of related expansive soil problems, e.g., rainfall-induced landslides and deformations of pavement.