By analyzing the characteristic of full binary tree, an equivalence definition was obtained. A decision algorithm of full binary tree completely based on height was provided by the equivalence definition. The algorithm solved the traditional deciding problem of full binary tree. The traditional method needs not only calculate binary tree height but also count branch node numbers. The new decision algorithm enriched the deciding methods of full binary tree. The application shows that the decision algorithm of full binary tree completely based on height runs accurately and the decision result is creditable.