Accelerating Rate Calorimeter (ARC) has been employed to study the decomposition of ammonium nitrate under 0.1 - 3MPa helium pressure. GC and MS analysis of the gaseous products indicated that the decomposion proceeds by the same mechanistic pathway up to 3 MPa applied pressure. Kinetic fitting of the ARC data have been done using BatchCAD package. There is a good agreement between the model predicted and experimental values. For the first time, independent Arrhenius parameters for two parallel reactions for AN decomposition are reported. The reaction mechanism for decomposition, the temperature range, and the Ea and A values are given in the paper and the results are discussed. The present study is the first report on the kinetic modeling of adiabatic decomposition data using BatchCAD(BC) as well as AN adiabatic decomposition under pressure.