Abstract: The completeness of the coherent state is proved by using the technique of integration within the ordered product （IWOP） ,where the integral variables z and z^＊ have been preformed independent transformation. Both the completeness and the property of the coherent state of the displaced Fock state D（z） │n〉 are also proved by using the IWOP.

Key words: IWOP, eigen state, Fock space, operator