With the Q Oilfield in the Tarim Basin as an example，according to the principle of material balance，the main controlling factors behind elastic flooding productivity of ultra-deep fault-karst reservoirs are analyzed from the reserves，energy，fluidity 3 aspects to explain the difference in elastic flooding productivity at different fault orders. The results show that the main controlling factors include the scale of fracture-cavity reservoirs，elastic energy of formations and flow capacity of fluids. These three factors，on the whole，all play a greater role at the main fault than at the branch fault and contribute more at the branch fault than at the secondary fault. There is a strong linear relationship of single-well controlled reserves with cumulative oil production，daily oil production，and staged cumulative oil production of a single well by elastic flooding. The products of initial formation pressure with the cumulative oil production and controlled reserves of a single well manifest as a straight line with a slope of approximately 1 on the logarithmic coordinate. The comprehensive elastic compressibility coefficient and the fracture-cavity reservoir scale have a greater influence on cumulative oil production than initial formation pressure. The stronger fluid flow capacity indicates the higher average daily oil production per well. For the greater elastic flooding productivity of ultra-deep fault-karst reservoirs，the fracture-cavity reservoirs with a large scale and a high level of formation breakage should be preferred in the early deployment of well locations，and single-well controlled reserves should be maximized in the middle and late stages of development.