Dictionary is a system that comes into existence under certain conditions. It is an entirety of some interrelated and interactive external elements. In this entirety, explicit elements are those can be directly cognized by readers, such as style, words collection, entry set-up, definitions, while implicit elements are those can not be directly erceived, such as philosophy and purpose of codification. It is the latter that plays the dominant role, controlling and guiding the former. In turn, the explicit elements implement and indicate the principle of implicit elements. All the explicit elements can be codified into the dictionary system. Generally, the main part of dictionary consists of three sub-systems, i.e. words and phrases system, words association system as well as definitions.