Abstract: The interaction between the parser and the grammar is the central issue in linguistics and natural language processing. How grammatical English long-distance wh-questions is processed is one of research purposes in the field of psycholinguistics and second language acquisition. This study is an attempt to explore the subject-object asymmetry in a theoretically panoramic way, and to identify what is the main factors of the difference in target structures' processing difficulty, and to make clear how the mechanism of language processing works, thus to make learners more effective in mastering English wh-questions.