Flower of Evil (1857) is Baudelaire's masterpiece, which also embodies his innovative spirit. One of the innovations is that he described the ugly phenomenon of big cities. In his works, the scenery in Paris is dark and mysterious, and it is the poor, the blind, prostitutes and even the ugly female corpse lying in the street that attracts the poet's attention. Baudelaire's description of ugliness and ugly things is of great aesthetic significance. He thinks there is beauty in ugliness. Contrary to the romantic view that nature and human nature are full of harmony and beauty, he advocates that "nature is ugly", natural things are "disgusting", evil is "innate", virtue is man-made and goodness is man-made; Evil exists in people's hearts just as ugliness exists in the center of the world. He thinks that to write ugliness, we should "discover the beauty in evil" and express the "spiritual turmoil in evil". Baudelaire often uses ugly images when describing people's mental state. Take Melancholy Four as an example, all the images in the poem are ugly: the pot cover, the black light, the damp prison, the timid bat, the rotten ceiling, the iron grating, the dirty spider, the spider web, the wandering ghost, the long hearse procession and the black flag. These disgusting, ugly and ominous images come one after another and fill the whole poem. They showed "mental turmoil". In a word, Baudelaire takes ugliness as beauty and turns ugliness into beauty, which is of innovative significance in aesthetics. This aesthetic view is one of the principles followed by modernist literature in the 20th century.
The second innovation is to express personal depressed psychology and write about the tragic fate of petty-bourgeois youth. It is unique to express this mentality of young people in poetry. Romantic poetry expresses the frustration of love, the loneliness of spirit and the sense of political loss, which is only the beginning in excavating people's deep consciousness. Baudelaire understands melancholy in a higher sense. He thinks that there is misfortune in typical beauty. Melancholy is the strongest voice to be expressed in Flowers of Evil. Judging from the whole collection of poems, the poet wrote about people's depressed situation in society. Melancholy haunts poets like the devil. Sadness is a morbid emotion caused by dissatisfaction with real life, and it also reflects that the younger generation of petty bourgeoisie is in a pessimistic and desperate state of mind because they can't find a way out. As the advertisements and comments in the first edition of Poems said, Flowers of Evil is "outlining the history of spiritual turmoil of modern youth" and "expressing the excitement and sadness of modern youth".