Hydrogen energy and hydrogen fuel cell vehicles have become the key development directions of countries around the world, and high-pressure hydrogen storage technology is the most widely used hydrogen storage method in hydrogen fuel cell vehicles. The on-board Type 4 hydrogen storage cylinders are an important hydrogen storage component of hydrogen fuel cell vehicles, and the storage medium is flammable and explosive high-pressure hydrogen. Therefore, the on-board Type 4 hydrogen storage cylinders determine the safety of the hydrogen fuel cell vehicles. When a hydrogen fuel cell vehicle accidentally catches fire, the high-pressure hydrogen storage cylinder may be exposed to localized fire, and gas cylinders are at risk of explosion before the pressure relief device (TPRD) operates. In this paper, the computational fluid dynamics method was used to establish the numerical calculation model of the on-board Type 4 hydrogen storage cylinders under localized fire, and the accuracy of the numerical calculation model was verified by the fire test results. Using the established numerical calculation model, the heat transfer characteristics of the 35MPa on-board Type 4 hydrogen storage cylinders after localized fire for 600s was analyzed, the effect of different filling media on the heat transfer characteristics of Type 4 hydrogen storage cylinder was studied. The results show: The temperature of the burning area of gas cylinder was significantly higher than that of other areas. The temperature growth rate of the gas in cylinder remained basically unchanged, and the maximum temperature of the gas reached 353K at 600s. As the burning time goes on, the growth rate of the gas pressure increased continuously, and the gas pressure reached 36.3MPa at 600s. And different filling mediums have little effect on the heat transfer characteristics of on-board Type 4 hydrogen storage cylinders.