Electrocatalytic nitrate reduction reaction (ENO3RR) is an alternative, sustainable, and environmentally friendly value-added NH3 synthesis method under ambient conditions relative to the traditional Haber-Bosch process; however, its low NH3 yield, low Faradaic efficiency (FE), low selectivity, and low conversion rate severely restrict the development. In this work, a Cu2+1O/Ag-CC heterostructured electrocatalyst was successfully fabricated by constructing a heterogeneous interface between Cu2+1O and Ag for selective electrochemical nitrate-to-ammonia conversion. The construction of the heterogeneous interface effectively promotes the synergistic effect of the catalytically active components Cu2+1O and Ag, which enhances the material conductivity, accelerates the interfacial electron transfer, and exposes more active sites, thus improving the performance of ENO3RR. Such Cu2+1O/Ag-CC manifests a high NH3 yield of 2.2 mg h-1 cm-2 and a notable ammonia FE of 85.03% at the optimal applied potential of -0.74 V vs RHE in a relatively low concentration of 0.01 M NO3--containing 0.1 M KOH. Moreover, it shows excellent electrochemical stability during the cycle tests. Our study not only provides an efficient catalyst for ammonia electro-synthesis from ENO3RR but also an effective strategy for the construction of ENO3RR electrocatalysts for electrocatalytic applications.