Based on the density of stales calculation of the concentration of oxygen vacancy in anatase semi-conductor, the model of anatase with different sizes and proper concentrations of oxygen vacancy were studied under the same condition.It was found that the anatase with relatively low oxygen vacancy shows better electric conducting performance by comparison of the relative average number of electrons in the conduction band , mobility and conductivity. So we arive at the conclusion that the lower the concentration of oxygen the better anatase can be prepared with heavy doping, and under the conditions of low tempeature and heavy oxygen vacancy, the conductivity of anatase semi-conductor is closely related to the concentration of oxygen vacancies, average number of electrons in the conduction band and the conductivity caused by scattering of oxygen vacancies.