Skeleton is a new notion designed for constructing space-filling curves of self-similar
sets. In a previous paper by Dai and the authors [1], it was shown that for all connected
self-similar sets with a skeleton satisfying the open set condition, space-filling curves can be
constructed. In this paper, we give a criterion of existence of skeletons by using the so-called
neighbor graph of a self-similar set. In particular, we show that a connected self-similar set
satisfying the finite type condition always possesses skeletons: an algorithm is obtained here.