While still in Hong Kong, Yu started to write books and pamphlets in Chinese commenting on the problems of intellectuals and democracy in the People's Republic. He was particularly tenacious over the years in presenting the achievements of Chen Yinke (1890–1969), the greatest modern scholar of Tang dynasty China, who was at first supported and then hounded to death by the revolution. His Harvard PhD thesis was published as "Trade and Expansion in Han China; a Study in the Structure of Sino-Barbarian Economic Relations" (Berkeley: University of California Press, 1967). Scrupulous and thematically relevant monographs, mostly published in Chinese, explored the role of intellectuals, especially early modern moral and political critics such as Fang Yizhi (1611–71), Dai Zhen (1723–77), and Zhang Xuecheng (1738–1801), who had been neglected in earlier scholarship. Yu also mastered the scholarship around "Honglou Meng", the novel known in English as "Dream of the Red Chamber", a masterpiece exploring the decline of a rich family at the height of the Qing empire in the late 18th century.