The International English Language Testing, which involves the assessment of four English skills has been selected as the preferred test to measure English language proficiency of non-native English speakers. In IELTS academic writing, grammatical range and accuracy, of which test-takers are required to use is one of the four criteria used to evaluate candidates’ written essays, which record a considerable occurrence frequency of clause complexes. In order to shape clause complexes, two basic kinds of logical relations in language are employed: parataxis and hypotaxis. They indicate how two or more adjacent clauses are connected to each other in dependent or interdependent ways. This study conducts an analysis of how clause complexes in IELTS academic exposition and discussion essays are formed by highly successful test-takers in light of functional grammar, thereby providing non-native writers with a better understanding of accurate parataxis and hypotaxis employment to produce good IELTS academic writing essays.