"Yen Fu's Letters to Xiong Yu Yang" is important material for studying Yen Fu in his later years. Based on Yen's manuscripts, we mainly carry out the discussion from these three aspects: Firstly, carding its circulation status of the Letters we consider that its research values are mainly embodied in the following three points: 1, it is the most important material for us to understand a true Yen Fu in his old age, and his fellows' ideology. 2, it provides the most reliable first-hand data for our textual criticism and clarifying Yen Fu's trace in his later years. 3, since these Letters been available, they have become an ideological weapon for the cultural conservatism.. By studying the Letters, we'll introduce and promote the research into the new cultural conservatism. Secondly, using the newly discovered K'ang Yu-wei's notes and commentary at the text, we'll do a preliminary discussion of the relationship between Yen and K'ang with the Letters as the center. And that Yen and K'ang converged on values in his later years, emerged from the "Chi fellow substandard" to a "like-minded". The key point of which is on Xiong Yu Yang and the Letters. They exchanged their ideas by this group of letters' writing. Xiong Yu Yang acted as an intermediary. Through writing of letters, Yen and K'ang were increasingly closer to each other in spirit. Letters became the medium and platforms for their exchange of ideas. Thirdly, we make some textual criticism to the relevant content of Yen Fu's Collections. Based on Yen Fu's manuscripts and the contents published on The Critical Review, we correct the errors, which provide credible historical information for in-depth research.