Controllable dopant of P-type impurity Ga in Si can be real-ized by open-tube mode and SiO_2/Si system. The segregation effect of silicondoped Ga in the process of the second oxygenation was systemically investigat-ed by SIMS and SRP. The rules of segregation of Ga and the equations of thelowest concentration value of Ga with time at near SiO_2-Si interface are ob-tained for the first time. It has settled the base to completely understand thediffusion of Ga and create the mode of open-tube Ca-diffusion.