[Objective] The effect of straw mulching(SM) on topsoil structure and air permeability were investigated to reveal the influences of straw mulching on topsoil physical properties and function in black soil sloping farmland. [Methods] This study was based on a long-term (7 years) field observation experiment of conservation tillage on black soil. Topsoil(0—10 cm) bulk density, porosity, saturated water content, field capacity, soil water stable aggregate and air permeability was analyzed and compared between straw mulching and conventional tillage(CT) field experiments. [Results] (1) The topsoil bulk density, saturated water content and field capacity of SM were higher than that of CT, while the soil total porosity and non-capillary porosity of SM was lower than that of CT.(2) Compared to the CT, topsoil water stable aggregate content (>0.25mm), mean weight diameter and geometric weight diameter in the SM soil was increased the by 10.41%, 45.28% and 22.58%, respectively, while soil air permeability was decreased by 30%. [Conclusion] Continuous 7-year SM improved the topsoil aggregate structure and water retention, but decreased the air permeability in black soil sloping farmland.