Topic sentence writing is an important component of academic writing. Through studying topic sentences in Chinese students’ English essays, this research aims to find out the frequency and the placement of topic sentences, the wording within topic sentences and the relationship between topic sentences and paragraph unity. In this research, 45 English essays written by Chinese students were collected from WECCL corpus and targeted topic sentences were selected out afterwards. Depending on Wordsmith 3.0, results related to topic sentences were generated including the frequency, the placement, the wording of topic sentences and the unity between topic sentences and supporting sentences. Results show that Chinese students have a good awareness of writing topic sentences and placing them at the beginning of paragraphs. However, Chinese students are not good at applying transitional phrases and expressing ideas objectively as academic writing requires. Moreover, paragraph unity in some Chinese students’ essays is poor. In addition, as a part of this empirical study, an interview about how to write topic sentences was conducted among ten Chinese students majoring in English in order to verify the results. Based on the responses from the interview and previous research, this research suggests that Chinese rhetoric convention and school instruction on writing are two major factors leading to the present results.