Abstract: C₂ hydrocarbons are important intermediates in petrochemical industry. Cryogenic rectification is broadly used to separate mixed C₂ hydrocarbon gas to obtain pure C₂ products. However, this process is very energy-consuming. Employing membrane separation technology to separate mixed gases can effectively reduce costs and energy consumption. Single-layer porous graphene membranes have great potential for mixed C₂ hydrocarbons gas separation because of their outstanding separation performance; however, relevant studies are scarce. Herein, molecular dynamics simulations are applied to study the effect on the efficiency and selectivity of C₂ hydrocarbons gas separation by single-layer porous graphene membranes with different pore sizes, pore shapes, and modified functional groups. The results show that the single-layer porous graphene membranes with pore sizes of 0.444—0.484 nm facilitate ethane retention with high ethylene passability. High gas passability and selectivity are determined for circular and oval pores, respectively. Oval pores with a short diameter of 0.510 nm and a long diameter of 1.164 nm are able to effectively pass ethylene molecules while retaining ethane molecules. A pore size of 0.596 nm with the pore being modified with two carboxyl groups can retain ethylene and pass acetylene. Our simulation results provide theoretical insights into the design of single-layer porous graphene membranes to separate C₂ hydrocarbons gases efficiently and selectively.