Electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) is an attractive approach to deal with the excessive emission of CO2 and to produce valuable fuels and chemicals in a carbon-neutral way. Many efforts have been devoted to boost the activity and selectivity of high-value multicarbon products (C2+) on Cu-based electrocatalysts. However, Cu-based CO2RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO2RR condition. To date, most reported Cu-based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu-based electrocatalysts for CO2RR. Here, a porous chlorine-doped Cu electrocatalyst is reported and exhibits high C2+ Faradaic efficiency (FE) of 53.8 % at-1.00 V versus reversible hydrogen electrode (VRHE). Importantly, the catalyst exhibited an outstanding catalytic stability in long-term electrocatalysis over 240 hours. Experimental results show that the chlorine-induced stable cationic Cu 0-Cu + species and the well-preserved structure with abundant active sites are found to be critical to maintain the high FE of C2+ in the long-term run of electrochemical CO2 reduction.