In this Paper we intnduce the nation of generalized trees. Because the chromatic polgnomial of a generalized trees can be easily found .we can write the chromatic polynomial of a general graph by use of the deleting -edgar-contracting-venices formula. The chromatic number of a generalized trees is exactly equal to the vertex number of the maximum clique contained in the generalics trees. So it i. POssible to find the chromatic number of a general graph by use of generalics trees. The necessary aam sutficient condition for a graph to be a gereralized tree given in the present paper is that the graph has no vertex subgraph ck(k≥4) whose venices are in a cycle. We also point out that a graph G is a generalized tree of tree sequence {1

p

1

..'

1

q} if f Ghas a cbromatic polynomial p(G

λ) =λ(λ-1 )'(λ-2)… (λ-r-1) (λ-r-2)'