Experiments of partial inerting on flame propagation of starch dust deflagration in a vertical duct were conducted to reveal the differences in flame structure evolutions. Particle pyrolysis and combustion behavior combined with time scale analysis are used to discuss the flame inerting mechanism. The results showed that the inerting process makes the flame front fuzzy, discrete and irregular. The thickness of flame reaction zone increases as O-2 concentration decreases, while the preheat zone decreases accordingly. The pyrolysis rate always controls the flame propagation process under inerting conditions. With the decrease of O-2 concentration, the control effect of pyrolysis rate is gradually weakened, and the effect of combustion reaction rate on flame propagation appears. A physical model of starch dust flame propagation under partial inerting is established, and the inerting process of dust pyrolysis and combustion on the flame structure evolution is further revealed. (C) 2020 Elsevier B.V. All rights reserved.