The Sea of Fertility, Yukio Mishima's last novel, is composed of four parts: Spring Snow, Runaway Horses,Akatsukinotera and The Decay of the Angel. The fourth part The Decay of the Angel, the end of the novel,also marks the end of Yukio Mishima's literary creation and life. Buddhism “reincarnation” concept is the clue involved from the first part to the fourth part of the novel. Despite of this, the hero Shigekuni Honta of the novel is haunted by a question all his life: does reincarnation really exist? Puzzled by this mystery, the hero rushes about for it. It can be said that this question is also raised by the writer Mishima. The interpretation of The Decay of the Angel, will help us to truly understand Mishima's literary theme and provide reference for our life.