The discourse analysis of Pharmaceutical English covers many fields of studies. In view of register analysis of systemic functional linguistics （SFL）, the pharmaceutical texts can be broadly divided into two categories：Pharmaceutical English for General Purposes and Pharmaceutical English for Special Purposes. Texts of different categories differ greatly from each other in terms of field, mode and tenor, which can not be ignored by the translators in employing strategies and skills. This study discusses the application of discourse analysis to translating pharmaceutical texts based on the register analysis of two instances of different types.