To study performance of the Chinese ancient timber buildings of Jiangnan area in the Song & Yuan dynasties in the progressive collapse, the finite element models of a typical Chinese ancient timber building and a corresponding building without Pu-zuo were established by the three-dimensional scanning survey for further Pushdown analysis, through which their main collapse mechanism and the effect of the Pu-zuo against the progressive collapse were studied. The results show that: For Chinese traditional timber buildings of the Jiangnan area in the Song and Yuan dynasties, when a column suddenly fails, the lateral components around it can provide multi-directional linkages to delay or prevent the progressive collapse. A “truss-like” structure is formed among the Pu-zuo to transfer the extra load when the progressive collapse happens, which effectively enhance the linkage and strengthen the alternative load path in the structure. Thus, compared with the timber building without Pu-zuo, the bearing capacity of the typical Chinese ancient timber building with Pu-zuo significantly rises, with increasing by 30%~50%; Compared with the failure of the middle columns, the failure of the side columns tends to result in the progressive collapse of the building. The results can provide a scientific basis for reinforcement against the progressive collapse of Chinese traditional timber buildings of the Jiangnan area in the Song and Yuan dynasties.