Oratorio is simple in form, but the meaning is colorful. There is no visual stage action performance, but the music can be very stunning. This research divided into two parts. The first part is mainly to study the history of the Oratorio. To learn more about the development and characteristics of the Oratorio, and to explore the life of Mendelssohn, which includes his family background, lifetime career and the importance creations, etc. The second part of this research is discussing Mendelssohn's “ Elijah” as an example. It begins with Mendelssohn's creative process and the premiere process, and then comes to understand the protagonist Elijah and the story of “Elijah” in the bible. The last part is to analysis four of soprano’s recitatives and arias, this could help interpretation during our practice.