The “Tianzihao” colony was built by the French Jesuits in the 1890s. As one of the earliest examples of the French Catholic Church’s mission in China, as well as the only case in Nanjing, it shows the historical scenes of Western missionaries in Nanjing 120 years ago. It is a demonstration of cultural exchanges between China and the West after China opened to the Western world in the late 19th century. In architectural style, the “Tianzihao” colony is Western-style townhouses, but a large number of traditional Chinese architectural technologies were used for it, and therefore it is characterized by Western space and Chinese technology. The “Tianzihao” colony was badly damaged during these decades, with a lot of decayed building materials and structures on the verge of collapse. Based on the historical research and technical analysis of the “Tianzihao” colony, this article explores the conservation strategies and methods of reusing the architectural heritage. In addition, this article is to study the characteristics of the times before introduction of Western architectural technology in Nanjing based on an analysis on the building technology used for the “Tianzihao” colony. The authors participated in the conservation and restoration project of the “Tianzihao” colony, and the objective of this study was achieved through some qualitative methods, including collection and analysis of archival data, analysis of old maps and photos, architectural mapping and a large amount of historical information found in the conservation process.