Oolitic limestone is one kind of typical chemical sedimentary rock, characterized with rich in ooids. In this paper, we will try to recognize Oolitic limestone based on the shape knowledge. Firstly it turned the RGB image into 8-bit gray image and made TV smoothing, then it made edge detection by Canny operator and edge fitting by Hough transform, finally it identified the Oolitic limestone grains. The experiments show that this method can achieve good results and meet the demand of oolitic limestone grains recognition.