Abstract: There is a great divergence of opinions towards the differentiation of paratactic or hypotactic relationship between the clauses in clause complexes in Mandarin Chinese.Taking a functional approach, this paper, based on the assumption that there is tactic relationship in clause complexes, advances that mood is the final criterion to distinguish the two types of dependent relationships.The paper takes an interrogative mood test to check whether both primary clause and secondary clause have mood choice by adding interrogative particles and changing tone sequence.The result shows that in paratactic clause complexes, both clauses have mood choice, while in hypotactic clause complexes, only the primary clause does.The study further demonstrates that Systemic Functional Linguistics is General linguistics and Appliable linguistics.