Abstract: A numerical simulation was conducted on the outlet velocity deviations of air-powder pipelines for different coal mills of a 1 000 MW ultra-supercritical once through boiler using computational fluid dynamics software. The influence of pipeline layout on the outlet velocity deviations was analyzed, and the effect of coal particle size, air-coal ratio and inlet air temperature on the outlet velocity deviations in air-powder pipelines was investigated. Results show that longer pipelines exhibit higher along-route losses compared to shorter ones, resulting in outlet velocity deviations. Moreover, as coal particle size distribution becomes more dispersed, internal flow disturbances in air-powder pipelines increase, leading to escalating along-route losses and decreasing outlet velocity deviations. Decreases in air-coal ratio and inlet air temperature also increase coal concentration in the pipeline, further enhancing along-route losses and reducing outlet velocity deviations.