The zirconia containing 12wt%Y2O3 thin films deposited by r.f.magnetron sputtering at 25℃ or 400℃, and then bombarded with Ar+ beam at room temperature were characterized with XRD before and after Ar+ bombardment.It is found that a series of phases formation and transformation happened, among them the mostimportant event is that T phase appeared after Ar+ irradiation andthe content of the T phase increased with the increase of Ar+ iondoses from 5×1015 to 6×1016 ions cm-2.