A gas separation process by 2D structure membranes has recently been considered. Some nanostructure membranes such as graphene have already been used extensively, but silicon carbide nanosheet (SiCNS) capabilities for gas separation have not been studied yet. Due to properties and structure of this nanosheet, it can be used for gas separation. with high permeability and selectivity. In this regard, the separation of alkane mixtures, such as methane/ethane mixtures, is important due to their many industrial applications. Accordingly, we studied the capability of a SiCNS membrane using molecular dynamics simulation technique for separation of the CH4/C2H6 mixture. To separate the gas mixture by a SiCNS membrane, some engineered pores were created on the surface of the membrane. At the same time, some of these pores were functionalized by appropriate chemical groups. The potential of the mean force of methane and ethane molecules was calculated in the path of the pores, and the calculations showed that gas molecules (methane or ethane) with a low potential of the mean force could easily pass through the pore. Also, the effect of the presence of multi-SiCNS layers was investigated. The results showed that in some cases, with increasing the number of SiCNS layers, the selectivity of the system was increased.