We investigate the microscopic properties of hydrogen impurity captured by Pb-vacancy in the ferroelectric perovskite through through first-principles seudopotential total-energy calculations. It is found that the ferroelectric polarization is not destroyed around an interstitial hydrogen impurity or around a Pb-vacancy, but by the complex defect H-V Pb . We suggest that it give an explanation to a well-known hydrogen-demage of the ferroelectric devices.