In this paper we bring forward an image edge similitude extent algorithm based on the steadiness character theorem of plane similitude graphics—similitude included angle theorem

and the algorithm is realized by constructing an AFMSDF (mean-square deviation function of angle fluctuation). The AFMSDF is used as a method of scaling the similitude extent of two different edge contours. This algorithm provides a reasonable method for graphic match

graphic search

efficient graphic similitude transform

and clustering

etc. Theoretical analysis and experiments indicate that the method is feasible.