Abstract: The fork-column Dou-gong timber-frame system is an important lateral force resistant system for multi-storey ancient building timber structures, and it is of great significance to study its lateral resistance. Taking the third layer side span in the deep direction of the fork-column Dou-gong timber-frame system of Dule Temple Guanyin Pavilion as the research object, the structural characteristic and lateral resistance mechanism are analyzed, and the lateral load-displacement analysis model is established. The expressions of model calculation parameters for different stress stages are determined, and the correctness of the model is verified by experimental study. Based upon this basis, analyzed is the influence of parameters such as vertical loading, height-span ratio, and wood elastic modulus on the lateral resistance performance of the fork-column Dou-gong timber-frame system. The results show that: the influence of vertical loading on the lateral performance of timber frame varies at different loading stages. Before the yield of a timber frame, the lateral stiffness increases with the increase of vertical loading, but the peak load decreases with the increase of vertical loading; the initial lateral stiffness and peak load of the timber frame increase with the decrease of its height and span; as the compressive elastic modulus of the transverse wood increases, the initial lateral stiffness of the timber frame increases, but at the same time, it also reduces its peak load, the yield and failure occur prematurely; increasing the compressive modulus of wooden elasticity along the wooden grain will enhance the bending resistance of the connecting beam, and then the lateral resistance of the timber frame will be improved. The research results can provide a theoretical basis for the lateral resistance analysis of ancient wooden structures.