VO2 thin films were prepared by DC magnetron sputtering on Si substrate,and then were annealed by oxidation. XRD and FITR were employed to study the effects of oxidational annealing on the crystal composition and infrared transmission properties of VO2 thin films. The results of analysis show that the VO2 crystal after annealing has changed from non-crystalline structure to crystalline structure. The size of monoclinic rutile structure VO2 (011) which has a better crystal orientation is bigger. After oxidational annealing,the VO2 thin films possess a obvious phase transition properties with uniform size of crystal,the phase transition temperature is 60.5 ℃,and the change range of infrared transmission rate at 3~5 μm and 8~12 μm has reached to 99%. VO2 thin films which have obvious phase transition properties in infrared transmission are ideal material for the research for protecting infrared detector from laser attacking.