Contemporary theory of metallic plastic deformation mechanism at low homologous temperatures is attributed to the physical processes of dislocations passing obstacles. Physically based deformation mechanism is generally considered as thermally activated motion of dislocations past obstacles and structural evolution of the obstacles. In order to verify the thermally activated deformation theory, stress rate change experiments, which give rapid stress changes, are conducted using pure aluminum at room temperature in this study. Incremental method is employed in the numerical simulation of above deformation mechanism. Excellent agreement is observed in the comparison between experimental data and numerical calculations, especially on the very abrupt change in strain rate at the stress rate change point. Sensitivity analyses are also performed to better understand the key parameters of both flow kinetics and structural evolution law. Simple kinetic model such as the regularly distributed rectangular obstacle is adequate enough. Obstacle structure is strongly influenced by the dislocation annihilation processes. Constant obstacle structure seems impossible to maintain once the loading condition changes.