A new invariant feature under affine transformation is given.And then,a new method for matching planar curves under affine transformation is proposed in this paper.First,the affine region is divided for obtaining a series of sub-region′s centroids.Then the triangles are constituted by using the whole contour′s centroid and sub-region′s centroids.The sequences of triangles′ area ratios are calculated and normalized.On the basis of the new invariant feature,a new recognition vector matrix is defined,and a different measurement function is defined too.Finally,the different measurement value between model curve and object curve is calculated,which can be employed to judge whether the model and object are matched.Theory analysis and experimental results show that the method is feasible,which can not only match different curves but also distinguish the objects with a similar shape according to different measurement values.