In this paper, modified 20 L sphere was used for the determination of the explosion venting of aluminum powder/air fuels, Fluent software was used for simulation to reveal the combustion mechanism. The results showed that the airtight accumulation effect gradually strengthened with the increase of the cracking pressure. Meanwhile, the maximum reduced explosion pressure and the flame length increased gradually accompanied by the flame changed from secondary/multiple flame type to single flame type. Additionally, the pressure field was reproduced by simulation. It demonstrated that the under-expansion jet was formed due to sudden change of pressure, density, temperature and Mach number between internal and outer of the vessel, which caused the turbulent kinetic energy at the vent to be much higher than that inside the vessel. The results at the conditions with vents of 70 mm and 50 mm in diameter had better accuracy and safety margin according to theoretical calculation. (C) 2020 Elsevier B.V. All rights reserved.