This research uses a simulation based on semiempirical computations to examine the property of graphene nanoribbon (GNR) as a gas sensor. GNR's interactions with two gas molecules (mithane, and water) have been thoroughly studied (both pure and defective). The adsorbtion of that two gas molecules was significantly higher in the case of malfunctioning GNR. The “Density of States (DOS)” diagram of graphene nanoribbon (GNR) before and after the interaction with gas molecules was discovered to be different. It's vital to look at the quantum capacitance when examining Graphene's electrical properties in order to comprehend the band structure and I–V characteristics. This study looked at quantum capacitance before and after gas sensing, and the results were produced with the help of simulation tools and equations.