Taken 32 Chinese university students of intermediate and high proficiency as subjects whose ages ranging from 23 to 25(average age=24.38), and adopted English passive sentences as experimental materials which were divided into two literal translation sentences and free translation sentences according to whether word order of sentences was changed or not in understanding them in Chinese, the study probed into the effect of second language proficiency on passive sentences processing under semantic complexity. The results showed: Reaction time and accuracy rate of subjects of high proficiency were faster and higher than those of intermediate subjects, indicating that proficiency could still predict the degree and level of English passive sentence processing in in the verb semantic complex situations. At this time the correct rate of the semantic violations is higher and it’s reaction time is shorter, than those of syntactic violations. Double violations and semantic violations caused N400 effect significantly; the correct sentence and syntactic violations did not induce negative N400. Behavioral data supported the effect of inter-Language Syntactic Similarity ---reaction time and accuracy rate on of literal sentences was faster and higher than those of free translation sentences, whereas ERP data indicated that N600 effect was larger in literal sentences, a larger P600 effect was observed in free translation sentences. These results second language proficiency could alter the effect of inter-Language Syntactic Similarity on second sentence processing.