The key problem in iris recognition is how to locate iris's position in an image. A new method of interior boundary of iris location based on active contour is presented. Firstly, a point in pupil called pseudo-center, which isn't required to be located at the real center of pupil, is detected by a method of gray projection. Secondly, several points spaced evenly around the pseudo-center are chosen as initial snake, and then the snake evolves until it gets the interior boundary of iris. Finally, two values are computed --one is the real center of pupil, which is expressed through the center of snake, and the other is the radius of pupil, the average distances between every control point of snake and the center. Experiments show that our method has better performance in speed and precision than Hough transform and daugman method. Moreover, our method is more robust because the pseudo-center is not rigorous.