This study approaches syntactic complexity from a relative point of view and examines how translation and interpreting students cope with relative clauses and passive constructions, two exemplifications of syntactic complexity in English–Chinese sight translation. A group of students (N = 23) took part in the study. The study consisted of three parts: an English reading span test, a sight translation task, and a baseline reading task. During the sight translation task, the participants sight translated English sentences with different degrees of structural asymmetry into Chinese in the single sentence context and the discourse context. During the baseline reading task, they silently read the English sentences and answered the comprehension questions. The participants' eye movements in the sight translation and baseline reading tasks were recorded as indicators of cognitive load. Three major findings were generated: (1) Syntactic complexity resulted in a significant increase in cognitive load during the sight translation task. The syntactic aspects of the target language were activated during the initial stage of comprehension, which favoured the parallel view of translation. (2) Although sight translation became more time efficient due to wider contexts, a larger amount of contextual information did not make word-based processing less effortful, as indicated by more fixations and the longer regression path duration in the discourse context. (3) No correlations were found between reading span and cognitive load in addressing syntactical complexity.