This study examines the referential context effect on second-language relative clause ambiguity resolution by proficient L1 Chinese learners who learn English as a foreign language (EFL) and investigates whether the ambiguity resolution process is constrained by individuals' working memory capacity (WMC). It presents a self-paced reading study and investigates L2 relative clauses ambiguity resolution in two phases. The baseline phase probes Chinese EFL learners' initial attachment preference when comprehending global ambiguous sentences without referential context. In the further experimental phases, each target sentence is preceded by a referential context with either neutral or NP-biasing information. We observe the change in reaction time spent on processing sentences and answering comprehension questions. Results showed that firstly regardless of WMC, proficient Chinese EFL learners employed a high-attachment parsing strategy when there was no referential context. Secondly, referential context facilitated sentence processing and comprehension, as demonstrated by decreased reaction times in critical region and on comprehension questions from neutral to biased contexts, with no significant difference in accuracy rates. Notably, the contextual effect was more pronounced when high-attachment contextual cues were present. Thirdly, working memory capacity modulated the ambiguity resolution process. Participants with different WMCs showed different parsing behaviors, and this difference manifested itself in both the interpretive and post-interpretive stages of processing. Participants with lower WMC had limited cognitive resources for processing ambiguous sentences, whereas those with larger WMC were more adept at resolving ambiguity in a context-dependent manner. These findings offer new insights into L2 shallow sentence processing as well as WMC constraints in L2 ambiguity resolution.