The comprehension of ambiguous relative clauses by second language (L2) learners has been a heated topic in psycholinguistics, but the debate is still ongoing as to whether L1 and L2 readers show similar attachment preferences. Importantly, the effects of emotionality on relative clause attachment in L2 are still underexplored. By employing self-paced reading tasks and offline attachment choice tasks, the current study explored the ambiguity resolution of relative clause (RC) attachment in second language from the perspective of emotion by conducting four experiments with 342 Chinese EFL learners. The results show that: (1) under the neutral condition, advanced Chinese EFL learners fail to show an NP2 attachment preference frequently reported by L1 studies, which lends support to the Shallow Structure Hypothesis; (2) under the emotional condition, due to attention and memory advantages, negative antecedents with greater biological relevance can enhance their topicality, and therefore are more likely to host the RC; (3) different patterns of RC attachment preferences between the online reading tasks and the offline attachment choice tasks could be attributable to the two tasks’ differences in explicitness, time course of RC attachment, and demands on working memory capacity. This study betters our understanding of the factors influencing attachment preferences in L2 relative clauses and extends research on L2 emotional word processing, offering a novel perspective for investigating L2 emotional word processing in sentential contexts.