A dynamical growth model of MBE (Molecular Beam Epitaxy) is discussed. A surface characterization method, i. e. HEED, is used to support this model. GaAs is taken as an example to investigate the MBE growth rate and its dependence on Ga flux by using the quadrupole mass spectroscopy. A suitable ratio of partial pressure of Ga to that of Al is studied theoretically and experimentally for growing Ga1-x Alx As materials with particular values of X. The dependences of doping concentrations in Si-, Sn-, and Be—doped GaAs on the temperatures of their effusion cells are given respectively.