In order to better understand the role of syntactic similarity in a code-switched sentence, the current study explored the effect of similar and different syntactic structures on Chinese-English bilinguals' intra-sentential switching costs. L2 proficiency and switching directions as factors that potentially intervene in bilingual performance were together explored to see if there was any interaction. We manipulated the degree of syntactic similarity by utilizing clauses in active voice (greater similarity) and passive voice (lesser similarity). The study conducted a self-paced reading paradigm as a more natural language reading processing. Results showed overall longer reading times for active sentences than passive counterparts, which supported a syntactic similarity impediment rather than facilitation. The impediment seemed to be predominant irrespective of L2 proficiency. Furthermore, syntactic similarity modulated the asymmetry of switching costs between forward (L1-L2) and backward (L2-L1) direction: word RTs for the 1st and the 2nd switched word yielded greater costs in L2-L1 condition, while greater costs in L1-L2 condition was observed in 3rd switched word RTs and average RTs. The present study observed syntactic similarity impediment rather than facilitation for Chinese-English bilinguals. Notably, syntactic similarity plays a predominant role compared to L2 proficiency, and modulates the asymmetry between switching directions.