In terms of the uses of urushi for architectural decoration and finishing in Northern China, the partitions of the Bower of Ancient Catalpa (Gu Hua Xuan) are an exceptional example. Typical samples from the objects were analyzed using various methods, such as optical microscopy, immunofluorescence staining analysis, X-ray fluorescence (XRF) spectrometry, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). In combination with literature on traditional lacquering and Qing Dynasty historical archives, the organic and inorganic materials, manufacturing techniques and repair history of the decoration were comprehensively described. For the partitions of the Bower of Ancient Catalpa, decorative layers of eight generations have been preserved. The initial materials of the coating are Chinese urushi mixed with tung oil. Black lacquer in different periods was obtained by adding carbon black and iron salt, respectively. For the original painting, the decoration layer followed a complete process:ground—fabric lining—plaster—black lacquer—colored lacquer—gold decoration; the method of repainting was relatively simplified and the original “homogeneous gold foil” was changed to two types of gold foils with different colors.