In most airbag systems, the gaseous mixture that fills up the airbag is produced by the fast combustion of a propellant in a combustion chamber called inflator. Since the process of gas production in the airbag inflator is a high-temperature combustion process, having a right understanding and precise control over the combustion in the airbag inflator has always been a challenge. In this paper, the numerical study of combustion process in a pyrotechnic inflator was carried out based on a Zero-Dimensional Multi Zones model. The parametric study show that the performance of inflator is more affected by the propellant characteristics such as mass, combustion index, and propellant temperature coefficient and is not significantly influenced by hardware elements of inflator. In order to simulate hybrid pyrotechnic inflator, the initial pressure of gas plenum was increased by 25 to 50 times. As a result, the performance both in combustion chamber and in discharge tank decreased. This lower temperature leads to a higher thermal efficiency.