Oxygen vacancies with different charge states in cubic LaAlO3 were investigated using first-principles calculation based on the density functional theory and generalized gradient approximation. In the presence of oxygen vacancy, extra level appears in the energy band gap. From the formation energies, it is found that oxygen vacancy is thermodynamically favorable under O-poor condition. Oxygen vacancies of and are the most stable charge states with the changes of the Fermi level position. Moreover, the oxygen vacancy in LaAlO3 has a negative U behavior and it is energetically favorable for the oxygen vacancy to trap two holes when the holes are injected into the oxide. Therefore, oxygen vacancy is a main source of charge traps in LaAlO3 high-k dielectric.