The paper focuses on a set of paper model (tangyang) fragments that were found during the conservation of Cuishang (Lush Scenery) Building located in the Garden of Longevity and Tranquility in the Forbidden City in Beijing. Through analysis of the historical construction and furnishing activities of Cuishang Building, paired with the detailed observation of the material and the technical and stylistic characteristics of the fragments, the authors interpret the function and the context of the original model and shed light on the use of a ‘toolbox’ for design in imperial China. This toolbox contains all kinds of design tools, ranging from wooden models and paper models to architectural drawings and the technical terminology describing parts of the buildings. Ultimately, this can help us to better understand the modes and rules and the high level of professionalism in design during the Qing dynasty.