In order to study the gas diffusion-transport law and the influence of ventilation on the gas concentration of high gas tunnel after blasting, an optimization blasting scheme under gas conditions was carried out, and a gas diffusion-transport characteristic near the working face was investigated under both ventilated and unventilated conditions in a project. The study shows that the residual rate of the blast hole and the utilization rate of the blast hole are above 90%, and the over-excavation control effect is better with an expected blasting footage of 1.2 m and an uncoupling coefficient of 0.76. Under the condition of unventilated condition by numerical simulation, the gas accumulation near the arch top and the arch waist at the tunnel's working face is severe as the gas concentration is close to 30%. Meanwhile, the gas concentration is higher in the area 7 m away from the working surface, and the gas concentration gradient is smaller in the area beyond 7 m after the gas state is stabilized. The gas concentration can be reduced to the safe range around 30 days after ventilation. However, gas accumulation quickly occurs at the arch foot and the arch waist on the other side of the air duct, especially the gas accumulation at the arch foot is more prominent, and the gas concentration is close to 20%. There is a ventilation blind area at the arch foot of the same side of the air duct, and the gas accumulates in a small range as the concentration is about 5%. The monitoring and prevention of the above areas should be strengthened. The field measured gas concentration distribution and gas influence range are consistent with the simulation results, and the research results can provide a reference for similar gas tunnel blasting construction and ventilation optimization.