Porous silicon oxycarbide (SiCO) is a novel class of nano-porous material with superior gas sensing performance. In this work, the amorphous porous structure of SiC5/4O3/2 is successfully reproduced by simulating the experimental etching process, and the gas sensing performance of porous SiCO at high temperature is investigated. The calculation results show porous SiC5/4O3/2 exhibits a much higher sensitivity towards H-2 than CO, NO2 and acetone at 773 K. Compared with the other three gases, H-2 absorbed system show shorter adsorption distance and more obvious increasing in density of states around Fermi level. Therefore, porous SiC5/4O3/2 shows a highly selective sensitivity toward H-2 at high temperature. Moreover, our results show the Si-C/O units are the major sensing sites of H-2 at high temperature, and the large diffusion coefficient of H-2 in SiC5/4O3/2 is related to the fast response of porous SiCO gas sensor. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.