This paper particularly analyzes some factors possibly disturbing iris localization in the iris image through the localizing pre processing. After establishing two dimensional projection of the edge rude field

the paper researches the relation between every dimension projecting characters and the tangled distributing traits in the edge rude field

and then acquires the possible good rude field of iris edge using the way of scout and crossing

finally calculates the exact iris boundary. After the comparing test and the analysis to the iris image database

the result shows that the robust algorithm can quickly and accurately complete iris localization and it is not sensitive to different filters worked on the pre processing of the localization.