针对气膜条件下厢式运输车厢体表面摩擦阻力减小的实验结果，分别提出边界层加厚理论、混合降速理论、边界层加厚 － 混合降速理论 3 种理论来研究空气介质中空气膜的减阻机理，建立了气膜条件下厢式运输车厢体表面气流摩擦阻力计算模型，定性对比分析了厢体表面在有气膜和无气膜条件下各自所受到的气流摩擦阻力． 结果表明，有气膜时摩擦阻力减小，这一结果与笔者前期的实验研究结果趋于一致，为气膜减阻在厢体表面减阻中的实际应用提供了理论基础．

According to the friction resistance decrease of van body surface observed by experiments in the presence of air film，three theories，namely the thickened boundary layer theory，the mixed deceleration theory and the thickened boundary layer-mixed deceleration theory，are put forward to explore the mechanism of air-film drag re-duction，and a model to calculate the friction resistance of van body surface in the presence of air film is estab-lished． Then，the friction resistances of van body surface with and without air film are qualitatively compared and analyzed，respectively． The results show that the friction resistance decreases in the presence of air film，which is consistent with the previous experimental results obtained by the authors． This research provides a theoretical foun-dation for the practical application of air-film drag reduction of van body surface．