At present, the fire performance of vehicles is highly concerned in domestic and international rail transit market projects , where the fire performance of the vehicle’s underframe is a crucial factor that restricts the fire safety of the entire rail vehicle. How to improve the fire resistance of vehicle underframe structure has become the focus and difficulty of vehicle fire engineering . This article introduces main international fireproof standards applicable for urban rail vehicles. Then, based on the typical underframe structures of urban rail vehicles stainless steel body, three refractory structure models on different underframe structures are established by using different fireproof insulation materials as underframe fillers. Moreover, fire resistance tests are conducted on samples of three underframe models to verify the effectiveness of those fire performance. As per the fire test results, the crucial indexes such as heat insulation, fire resistance, temperature rise curve, fire resistance time and material cost of different filler insulation materials are compared and summarized. Finally, the standardized and modular design specification is suggested on refractory underframe structures in urban rail vehicles.