A new kind of iris image preprocessing algorithm was presented to ameliorate the limitation of the existing iris image preprocessing algorithm.The iris was located accurately so that the processed image is invariant for translation,rotation and scale.Under the same experimental condition,104 iris images comprising an iris image database were preprocessed.Our algorithm only costs seven minutes and fifty seconds while the algorithm of Daugman costs about one hour,which proves that the run speed of our algorithm is nearly eight times faster than that of the Daugman's and it can overcome the shortcomings of costly computation that the existing algorithm has.