Abstract: The chlor-alkali process plays a key and irreplaceable role in the chemical industry because of its use in various industrial processes. However, the low selectivity and efficiency of the reported chlorine evolution reaction (CER) electrocatalysts obviously hinder its practical use. We report a simple method for the controlled growth of high-performance CER electrocatalysts by first growing cobalt hydroxide on the surface of carbon cloth, followed by the in-situ growth of graphdiyne (GDY/Co(OH)₂). As expected, the as-synthesized catalyst has a small overpotential of only 83 mV at 10 mA cm⁻², a maximum Faradaic Efficiency (FE) of 91.54%, and a high chlorine yield of 157.11 mg h⁻¹ cm⁻² in acidic simulated seawater. Experimental results demonstrate that the in-situ growth of GDY on the Co(OH)₂ surface leads to the formation of heterointerfaces with strong electron transfer between GDY and Co atoms, resulting in a higher conductivity, larger active specific surface area and more active sites, thereby improving the overall electrocatalytic selectivity and efficiency.