TiO2　nanotube　arrays　were　fabricated　by　anodization　of　the　Ti　foils　in　aqueous　phosphoric　acid　and　sodium　fluoride　solutions　at　20V　under　ultrasonic　field.　The　resulting　nanotubes　had　the　similar　tube　diameter　(100nm)　and　the　similar　wall　thickness　(15-20nm).　The　tube　lengths　of　the　nanotubes　anodized　for　1h,　3h　and　7h　were　600,1000,　900nm,　respectively.　Employing　a　500W　high-pressure　mercury　lamp　as　the　light　source,　the　open-circuit　potential　and　the　photocurrent,　the　flat　band　potential　and　the　charge　carrier　densities　of　TiO2　nanotubes　arrays　annealed　at　500　degrees　C　were　analyzed　by　the　open-circuit　potential　curves,　the　voltammetry　curves　and　Mott-Schottky　plots.　The　results　showed　that　the　photocurrent,　the　flat　band　potential,　the　charge　carrier　densities　of　the　resultant　samples　reduced　with　the　increase　of　oxidation　time.　The　decrease　of　photocurrent　density　was　more　than　that　of　the　open-circuit　potential.　It　can　be　ascribed　to　partial　fracture　and　detachment　of　the　nanotubes　and　the　growth　of　the　barrier　layer　with　the　inrease　of　anodization　time,　which　led　to　the　augment　of　the　charge　transfer　resistance　and　the　decrease　of　the　charge　carrier　densities.