Composite propellant contains Ammonium Perchlorate (AP) as a chief ingredient and its combustion characteristics are mostly controlled by the fraction and particle size of AP present in it. The deflagration behavior of AP is studied to get an insight into complex processes in composite propellant combustion. One specific characteristic of AP is that it does not exhibit self sustained combustion below a certain pressure commonly known as low pressure deflagration limit (LPDL) which is the subject of current study. This paper reports the computational studies that have been carried out to explore the effect of thermal properties on LPDL of AP. Two cases have been explored which differ in the manner in which the heat flux is imposed at the surface. Case I corresponds to constant incident flux which is cut off sharply, while Case II corresponds to constant incident heat flux followed by linear decrease to zero. The computational results obtained are in good qualitative agreement with the experimental results for case I. It has been shown through computations that combustion remains stable near the LPDL region. © 2017 Combustion Institute. All rights reserved.