In late-nineteen century, many different music styles have sprung up in Europe. In this trend of varieties, how to define oneself was a question that every musician in that era should face.

Frederick Delius is a productive musician, his orchestral pieces and theatre music got favourable comments by the audiences. Frederick Delius was born in England, and had received his music education in Germany, then settled down in France for the rest of his life, various culture had the significant impact on his musical style .

This paper is divided into five chapters. the chapter one is the introduction of motivations, purposes, range and methods about this research. In the chapter two, the author introduces Frederick Delius' life, background, and summarize his personality and composing styles. The chapter three is the analysis of Frederick Delius’ Sonata in B, Op.posth. The chapter four is the interpretation of this sonata. The chapter five is the overall conclusion.