A basic analysis is given to understand how a continual irradiation of atomic hydrogen (H) during molecular beam epitaxy (MBE) of GaAs could result in production of atomically smooth surfaces, abrupt heterointerfaces, and high-quality epitaxial layers as required for many applications. Some interesting results related to the atomic-scale growth mechanisms and atomic interactions are presented, and a growth model is proposed for atomic H-assisted homoepitaxial MBE of GaAs. It is thought that atomic H is an effective surfactant reducing the surface and total energy of GaAs (001), and acts to provide favorable kinetic and energetic pathways to promote an ideal layer-by-layer two-dimensional growth mode.