The current study focused mainly on the role of the linguistic complexity of IELTS writing Task 2. In other words, it investigated the differential effects of two interrelated linguistic complexities of writing Task 2 on the three levels of discourse representation and what IELTS candidates perceived through analyzing IELTS writing topics both at the sentence and idea levels was taken into consideration. The participants were 10 Iranian modest and competent users of English. A total of 10 writing topics, randomly selected from 70 Task 2 of Cambridge's passed administered IELTS writing tests (every 7th) was the main instrumentation of a five-week period of data collection. The data analyses were based on a codification scheme adapted from, and a software analyzer known as the Lexical and Syntactic Complexity Analyzer. The effects of lexical and syntactic complexity of writing task on CAF of language production were calculated through separate statistical analyses. The results of the study revealed that lexical complexity applied in IELTS writing topics had a greater influence on IELTS candidates` understanding of the IELTS writing topics than syntactic complexity. Furthermore, Iranian IELTS candidates were initially attracted to the situational representation of IELTS writing topics.