Abstract: To explore inorganic mineral layer formulation for flexible fire-resistant cables, effects of dolomite, sodium silicate, Mg(OH)₂, Al(OH)₃ and mass fraction of dolomite on the density, viscosity, thermogravimetric performance and thermal insulating properties of fire-resistant mud were investigated. Thermal insulating properties of the optimized fire-resistant mud was furtherly validated by encapsulating it onto finished cables. Results indicated that dolomite synergized with sodium silicate could enhance thermal insulating properties via endothermic decomposition and the formation of a dense shell structure respectively in the four materials. Based on this core material system, ratio optimization experiments revealed that when mass ratio of sodium silicate to dolomite was 100:200, the fire-resistant mud could achieve superior thermal insulation and structural integrity. Subsequently, developed coating was applied to the corrugated isolation layer of NG-A BTLY cable samples. After combustion at 950 °C for 10800 s, the fire-resistant layer of the cable could remain intact, and the cable could pass the voltage withstand test, demonstrating that the developed fire-resistant mud could serve as an effective thermal-oxygen barrier during combustion.