During the construction of the Wushan extralong tunnel, several environmental problems emerged. These included the large release of pollutants in the working space, inefficiency in replacing sewage wind, and dangerous local concentration of harmful gases. To address these challenges, the dynamic diffusion law of pollutants such as CO and dust is examined. This analysis is based on field monitoring data and employs a fullscale numerical simulation method. Moreover, the hindering effect of lining trolleys on dust diffusion is explored under various conditions, including singlehole tunneling, doublehole synergistic tunneling, and within a long ventilation chamber. The results reveal the following findings: (1) The air flow field stability is affected by the longitudinal return air velocity of the tunnel, leading to relatively large fluctuations in the air flow field within the 0.5~0.7 m/s range, hindering the pollutants′ discharge. (2) Pollutant is ultimately discharged synchronously by decreasing the overall concentration when CO diffuses. The 900 s ventilation proves sufficient for the allowable CO concentration within 200 m of the working face during both single and doublehole tunneling conditions. (3) The presence of a trolley has a remarkable blocking effect on the blasting dust diffusion, resulting in an approximate 42% lower overall dust reduction rate in the section with secondary lining trolleys compared to the construction section without the trolleys. Moreover, the dust reduction efficiency without a trolley is approximately 2.5 times higher than that with a trolley.