This work explores the possibility of ammonium polyphosphate (APP) as the inhibitor for starch dust deflagration. The flame propagation behaviors of starch dust samples are investigated in a half-closed vertical duct. Flame images and temperature are recorded by high speed camera and fine thermocouples, respectively. The high speed photographs indicate that flame propagation and flame luminous intensity of starch dust at the initial stage are greatly suppressed by APP. Maximum temperature values are also significantly decreased by APP. Thermal decomposition behavior and kinetics of starch samples are studied to ascertain the influence of APP on the decomposition activation energy. The combustion heat release of starch samples are tested by pyrolysis combustion flow calorimetry. Inhibition mechanisms of APP on starch dust deflagration are concluded according to the results of flame propagation, thermal decomposition kinetics and heat release. This work proposes a new strategy for exploration of inhibition mechanisms of dust explosion. (C) 2019 Elsevier B.V. All rights reserved.