Support settlement and cable slippage of a long-span suspension bridge may occur when it is subjected to extreme events. The evaluation of effects of support settlement and cable slippage on the remaining capacity then becomes important before making a retrofitting decision. However, it is difficult to conduct such an evaluation on the prototype bridge. This paper therefore presents experimental and numerical studies to examine the effects of support settlement and cable slippage on the structural performance of a long-span suspension bridge through a testbed, which include a laboratory-based model and an updated finite-element (FE) model. Four support settlement cases are experimentally studied with two on anchorage settlements and two on tower settlements. Main cable slippage at the top of towers is then investigated experimentally in two opposite directions. Both support settlement cases and cable slippage cases are also simulated using the corresponding FE model, and results are compared with those from the tests. Finally, numerical studies are conducted to investigate cable slippage caused by large support settlement. The results show that the experimental and numerical simulation using the testbed is an effective way to assess the effects of support settlement and cable slippage on long-span suspension bridges.