In the article, the author tries to find out the main factors that affect the subject's vocabulary acquisition by an investigation. It is concluded that vocabulary acquisition models and strategies are something external, what really works upon vocabulary acquisition is the intermediary system of cognition including the knowledge structure and abilities structure of the subject. The richer the intermediary system is, the greater the subject's cognition will be, which will contribute greatly to the subject's vocabulary acquisition. Meanwhile, the components of the knowledge structure and abilities structure are explored, furthermore, it studies how the components as the intermediate means work upon vocabulary acquisition in an interactive manner.