After the failure of Great Revolution in 1927，Mao Dun withdrew from the political arena，but the cause of this failure occupied his mind.In his subsequent novels and papers，petty bourgeoisie became one of his core themes.In Mao Dun's view，petty bourgeoisie played an indispensable role in the practice of revolution and the creation of revolutionary literature.Therefore，it was not just a parasitic class as the revolutionary literati see it，but had its own subjectivity.Mao Dun's viewpoint brought on fierce challenge from the revolutionaries .In the argument，Mao Dun began to adjust his position，intentionally concealing and revising his emphasis on petty bourgeoisie's subjective consciousness，and accepting the revolutionary literati's demand that historical inevitability should be represented in his writing.Mao Dun's transformation was an essential precondition for him to join the League of the Left-Wing Writers and to become one of its leaders.