In this work, adsorption of Cu2O on a graphene which leads to production of Cu2O–GS nanosensor and H2S adsorption on it are computationally investigated. Adsorption energies, density of state (DOS) and room-temperature electrical conductance of Cu2O–GS are calculated. Then a comprehensive discussion on obtained results is presented. Results show that adsorption of Cu2O on GS leads to 2 separate configurations. DOS of both configurations is plotted and the difference between the configurations is explained. Next, adsorption energies of both configurations after H2S adsorption are investigated. DOS of Cu2O–GS with and without adsorbed H2S are compared and it is shown that, according to the considerable variation of DOS after adsorption, Cu2O–GS is an applicable nanosensor for H2S detection. Then electrical conductance at room temperature is calculated to investigate detection capability of this nanosensor. The results illustrate that electrical conductance of the nanosensor is significantly increased by H2S adsorption. Obtained results are in good agreement with reported experimental results.