To investigate the stress-strain characteristics and hydro-mechanical coupling behaviors of unsaturated cohesive soils under static and cyclic loading, an elastoplastic two-surface model for describing the hydro-mechanical coupling behaviors of unsaturated cohesive soils under constant matric suction was established in the framework of plastic incremental flow theory. Considering the typical soil-water characteristics of unsaturated soils, based on the Barcelona basic model (BBM) and the plastic hardening rule suggested by Li and Meissner, the stress-strain characteristics and hydro-mechanical coupling behaviors of unsaturated cohesive soils under cyclic loading were described through the evolution of bounding surface and loading surface in stress space. Taking into account of the influences of initial degree of saturation, initial pore ratio, matric suction, net confining pressure, and dynamic stress amplitude, the model was verified by utilizing the previous research results of isotropic compression and static and cyclic triaxial tests. Comparisons between simulation results and experimental data show that the proposed model performed well in simulation. In addition, in order to examine the rationality of the model, several typical hydro-mechanical coupling behaviors of unsaturated soils under cyclic loading were predicted based on the test data. Results show that the proposed model could properly simulate and predict the hydro-mechanical coupling behaviors of unsaturated cohesive soils under static and cyclic loading with constant suction.