One Conclusion on the Essential Singularity of Analytic Function

In the article, the isolated singularity, removable singularity, zero, pole, essential singularity and other concepts and properties were used; Two lemmas on the isolated singularity were proved first, and to use these lemmas, one property of essential singularity was proved then. Key words: Analytic function; Isolated singularity; Essential singularity; Laurent expansion