Tongue diagnosis is an important method in TCM.Teeth marks are objective indexes of the diagnosis of qi deficiency.One method on teeth marks recognition is based on detecting the size of concave regions.The concave regions are caused by the bending of the tip and margin of the tongue, and the lip shades are easy to be misjudged into teeth marks.The pose and asymmetry of the tongue body also affect the judgment.Another method to identify teeth marks is to calculate concavity and convexity of the margin of the tongue.The narrow and long concave regions whose concavity is not deep are easy to be misjudged into teeth marks.Accordingly, this paper proposed a new method to extract teeth marks by calculating the slope of the margin of the tongue and the length and degree of the concave regions.Experimental results demonstrate the effectiveness of the method.