The electrochemical CO2 reduction reaction (CO2RR) to added-value C2+ products is a worthy way to effectively reduce CO2 levels in the atmosphere. Cu nanomaterials have been proposed as efficient CO2RR catalysts for producing C2+ products; however, the difficulties in controlling their efficiency and selectivity hinder their applications. Herein, we propose a simple routine to construct a graphdiyne (GDY) supported Ag-Cu nanocluster as a C2+ product-selective electrocatalyst and optimize the composition by electrochemical performance screening. The synthesized Ag-Cu nanoclusters are uniformly distributed on the surface of GDY with particle sizes constricted to 3.7 nm due to the strong diyne-Cu interaction. Compared to Cu/GDY, Ag-Cu/GDY tandem schemes exhibited superior CO2RR to C2+ performance with a Faraday efficiency (FE) of up to 55.1% and a current density of 48.6 mA cm-2 which remain stable for more than 33 hours. Theoretical calculations show that the adsorption energy of CO is much higher on Cu (-1.066 eV) than on Ag (-0.615 eV), thus promoting the drift of *CO from Ag to Cu. Moreover, the calculations indicate that the key C-C coupling reaction of *CO with *COH is more favored on Ag-Cu/GDY than on the original Cu/GDY which contributes to the formation of C2+ products. Our findings shed light on a new strategy of combining a GDY support with a tandem catalytic scheme for developing new CO2RR catalysts with superior selectivity and activity for C2+ products.