Abstract: For50 years, HU Shi had kept his diary which concentrated on current affairs, his feelings and academic ac- tivities. His existing diary has lost over ten periods with accumulative total of over ten years. Such lost parts are all about the above three aspects. His comments on the current situation might have been different from those of other people, or might have been contradictory with the future development. His emotional experience was personal privacy which would inevitably cause unexpected disputes. And his academic views would change because of new materials’ discovery and variation of his own conception. Once he found any contradiction with the fact, his simplest solution is to conceal or give up his view. For the“new studies of A Dream ofRed Mansions”, the two years of1921 and1927 were vitally important. However, his diary lost one of them and we may find answers to many mysteries in it.