Polyurethane (PU), as a kind of advanced polymer material, owns high tensile strength and high failure strain, and has been extensively used in aerospace vehicles. It is usually subjected to complex loading conditions in service. It is thus of significant importance to investigate into its complex mechanical response and underlying mechanisms under wide strain rate range for ensuring its service safety. In this study, polyurethane-matrix composites were synthesized with various soft-phase to hard-phase ratios of 1:1.5, 1:1.75, and 1:2, respectively. Tensile experiments were conducted under three strains rates loading for Mullins effect, using an electronic universal testing machine. The machine owned an attached digital-camera extensometer, which was used to measure real time displacement of two points marked on specimen during cyclic loading and unloading, and the accurate strain was obtained accordingly. Then stress-strain curves and hysteresis loop characteristics were obtained. Series of analysis was performed on its strain rate dependence and energy dissipation characteristics. Meanwhile, the strength dependence on the hard-phase fraction and strain rate was determined. The equivalent unit cell model was introduced to numerically model the microstructural evolution of PU composites, and some damage mechanisms was proposed with the aid of cohesive modelling. This work could provide an experimental basis for the application of PU in complex loading conditions.