The University of Nanking, founded in the early 20th century by an American mission in Nanjing, China, boasts a unique blend of Chinese and Western architectural styles, making it a valuable subject of research. Currently part of Nanjing University’s Gulou Campus, it has been designated a National Key Cultural Relics Protection Unit by the Chinese government, which has also formulated a protection plan for the historical district of Nanking University. This paper uses this site as a case study, employing methods such as historical document review, on-site investigation, and architectural surveying to reveal a “growth-oriented” coordination mechanism between heritage preservation and development within the context of historical campus expansion. This mechanism involves maintaining the original spatial layout through adaptive reuse, presenting a development model of “new branches sprouting from an old trunk.” The study points out that campus expansion is the root cause of the “new versus old” contradiction in historical campuses, while the need for functional upgrades in school buildings is the driving force behind heritage preservation. Coordinating the development and functional optimization of new and old spaces can effectively enhance the vitality of historical campuses and achieve a balance between campus expansion and heritage preservation. This research provides a practical Chinese solution for the sustainable development of similar historical campuses.