The mortise-tenon beam-column joint in ancient Chinese timber buildings would be loosened during earthquakes, multiple columns in the same floor would rock together, achieving a seismic isolation system to counter drastic effects from earthquakes, and this type of flexibility-based aseismic design is noticeably different from that of the current self-centering rocking systems. Incidentally, the Du Jiang Weir was a famous ancient disaster prevention & irrigation project, whose function has been resiliently maintained well for more than two thousand years. The design concept in the Du Jiang Weir is believed to be influential and instructive to the design of ancient timber buildings. In this paper, the design concept and engineering practice in the Du Jiang Weir are analyzed, and the ancient craftsmanship spirit is summarized as respecting and utilizing the nature resource. Bearing this spirit in mind, the design concept and engineering practice in ancient timber buildings are reexamined carefully, and its flexibility-based design logic can be associated with its enhancing seismic resilience, which is achieved by converting proper energy during earthquake into beneficial cyclic excitations. This paper tries to summarize the superior aseismic design concept of ancient Chinese timber buildings with “Flexibility, rocking, impact, and converting”, and it may provide reference for ancient timber building conservation and resilient aseismic design of new precast segmental structures.