Chemical fixation of carbon dioxide (CO 2 ) into value-added organics is regarded as a competitive and viable method in large scale industrial production, during which the catalysts with promoting CO 2 activation ability are needed. Herein, we proposed an in-plane heterostructure strategy to construct Lewis acid-base sites for efficient CO 2 activation. By taking ultrathin in-plane Cu 2 O/Cu heterostructures as a prototype, we show that Lewis acid-base sites on heterointerface can facilitate a mixed C and O dual coordination on surface, which not only strengthen CO 2 adsorption, but also effectively activate the inert molecules. As revealed by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and quasi in-situ X-ray photoelectron spectroscopy (XPS), Lewis acid-base sites could readily activate CO 2 to •CO 2 - species, which is the key intermediate radical for CO 2 fixation. As a result, abundant Lewis acid-base sites endow Cu 2 O/Cu nanosheets with excellent performances for dimethyl carbonate generation, a high conversion yield of 28% with nearly 100% selectivity under mild conditions. This study provides a model structure for CO 2 fixation reactions.