The finite element analysis model of heat conduction of gun barrel in the process of automatic mechanism firing was established according to the characteristics of gun barrel subjected to high frequency and high temperature impact under the condition of continuous firing. Based on the combination of heat conduction theory and finite element method, the variation of the temperature data of the inner and outer wall of the barrel is analyzed under different projectile numbers, different barrel wall thicknesses and different launching modes. The analysis can provide some guidance for the thermal capacity design of the automatic fuselage tube.