Iris annular line detection in the gray image directly with the edge detection operator will lost a lot of useful information, and false rate and missing rate is high, due to the signal intensity of iris annular line is weak compared with the background and the background image texture is very rich and the gray value of the annular line is not completely continuous. Thus, an iris annular line detection method is presented in this paper on the basis of analyzing the features of the iris annular lines. Firstly, the two part of the annular areas are selected as the region of interest due to the annular line position is fixed in the iris image; Secondly, the vector weighted line detection operator is designed to transform the random nature of the dominant signal into the adaptive weighted value, and the vector image is transformed into the single channel image with the most prominent edge information. Afterwards, the line detection matrix is designed to detect ROI according to the line characteristic distribution of annular line. Finally, nonannular lines are eliminated by shape factors of the binary images and the annular lines are detected. The method is used to detect 1921 lines that were artificially marked in our gallery, and the detection accuracy is up to 91.78%．The experimental results show the proposed method is suitable for detecting the iris annular lines from the visible iris images compared classic edge operators.