A planar point set X is called a k-distance set if there are exactly k distances between two distinct points in X. Let d(x,y) be the distance of any two distinct points x,y. Let diameter D=D(X) be the longest distance of X. The diameter graph DG(X_D) is composed of all diameters in X, where X_D is the set of its endpoints. In this paper, the configuration of the diameter graph DG(X_D) is discussed when X is a 7-distantce set. It is proved that the endpoint set X_D is the endpoint set of the regular 11-sided polygon when the diameter graph has 11 cycles based on the characteristics of DG(X_D) containing at most one and only odd cycle and the diameter specialty.