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Conversion of CO2into high-value products using electrochemical CO2reduction (ECR) technology is an effective way to alleviate global warming and reach carbon neutrality. The oxygen vacancies in heterogenous catalysis are generally considered as a powerful method to enhance the performance of ECR by promoting CO2adsorption and activation. However, the extent of defects in oxygen vacancies-activity relation has rarely been studied. Herein, we prepared Cu-Cd bimetallic catalysts with adjustable oxygen defect degree by controlling the amount of cadmium addition. Fourier Transform infrared spectroscopy characterization results reveal that the formation of oxygen vacancies is attributed to the asymmetric stretching of Cu-O by the addition of cadmium. Electrochemical results show that the oxygen defect degree can modulate the selectivity of ECR products. A low degree of oxygen defects (CuO) is generally associated with lower product Faraday efficiency (FEC2/FEC1≈ 114%), but overabundant oxygen vacancies (CuO2.625-CdO0.375) are not entirely favorable to improving ECR activity (FEC2/FEC1≈ 125%) and single selectivity, while an appropriate degree of oxygen vacancies (CuO2.75-CdO0.25) can facilitate the ECR process toward single product selective production (FEC2/FEC1≈ 296%). The theoretical calculation showed that the O vacancy formed on CuO and the interface between CdO and CuO were conducive to enhancing the formation of *COOH intermediate and promoting the generation of ethylene products. This study provides a new approach and insight into the selective production of single products for future industrial applications of ECR.