Translation purposes exist in two hierarchical levels: internal purpose and external purpose. Internal purpose, purpose inherent in and inalienable to translation, concerns the “essence” of translation and is characterized by stability; External purpose, purpose imposed on translation by social circumstances, concerns the “use” of translation and is characterized by instability. On the behavior chain of translation, the internal purpose and external purpose exist in a relationship of means and aims while, the external purposes of translation is realized through the realization of the internal purpose. The internal purpose of translation is “understanding”, and should be “understanding”; “understanding” is the very purpose that makes translation what translation is, and is therefore significant ontologically.