A mechanism of low temperature silane combustion has been proposed in the present work based on the assumption that a trace amount of water vapor helps the occurrence of spontaneous ignition at room temperature. This assumption has been made based upon the fact that the combustion product of silane influences positively the occurrence of spontaneous ignition. Energetic calculation of the reaction path way for low temperature silane combustion also supports this assumption [Kondo et al., 1999]. A numerical model has been constructed which can interpret the spontaneous ignition limit at room temperature, the ignition delay times, and the second explosion limit of silane mixtures simultaneously.