English writing instruction is an important part in college English pedagogy. Traditional way of teaching English writing lays much emphasis on word, grammar and sentence rather than the level of discourse. Under the traditional way, the students have difficulties to yield well-organized and coherent compositions. Theme Theory provides a theoretical foundation for a new method of teaching English writing. Thematic structure of the text is closely with the textual organization and the application of Theme Theory in teaching English writing helps improving students' writing coherence and overall writing proficiency. This paper gives an experiment on the application of Theme Theory in teaching English writing and attempts to verify the validity of the application of Theme Theory in the writing pedagogy of our college English.