:In this paper, we make use of the minimum root of adjoint polynomial of graph G, to find out two classes graphs which are irreducible, (G) = (G) + 1 and R(G) = -2 and the complements of these graphs are chromatic unique .

• 利用图G的伴随多项式的最小根的性质，通过比较伴随多项式的末项的方法，找到了两类 n 个点n+1 条边且 R(G)= -2 的图簇，其补图是色唯一的。