Studying the complexity of language has attracted the physicist's attention recently. The methods borrowed from the statistical mechanics; namely, the complex network theory, can be used for exploring the regularities as a characteristic of complexity of language. In this paper, we focus on the authorship identification by using the complex network approach. We introduce three metrics which enable us for comparison the author's writing styles. This approach was previously used by us for finding the author of unknown book among collection of thirty six books written by five Persian poets. Here, we select a collection of one hundred and one books of nine English writers and quantify their writing styles according to our metrics. In our experiment, Shakespeare appears as the best author who follows a unique writing style in all of his works.