Akutagawa Ryunosuke’s short story Rashomon has always been a hot topic of critics because of its rich ethical connotation and artistic characteristics. From the perspective of ethical literary criticism, this paper attempts to analyze the internal logical relationship between the spatial narrative, the metaphor of the festering pimple and the ethical choice of the protagonist. The spatial narrative of Rashomon carries rich ethical meaning and expresses the ethical theme. The festering pimple on the servant’s right cheek is an important prop by which the author expresses the change of ethical consciousness, and it is also a metaphor of the animal factor that becomes gradually externalized. Finally, The servant’s ethical choice to be a thief mirrors the ethical confusion that Akutagawa experienced before and after writing Rashomon, and his resistance to the feudal familial system that opresses human nature.