Electrocatalytic CO2 reduction to multi-carbon (C2+) products provides a promising route for converting CO2 into value-added chemicals and fuels, but achieving high C2+ selectivity for Cu-based catalysts remains challenging because of sluggish C–C coupling, competitive hydrogen evolution, and the complex interfacial microenvironment. Herein, four representative N-containing polymers, polyvinylpyrrolidone (PVP), polyaniline (PANI), polyethyleneimine (PEI), and polyetheramine (PEA), were introduced onto Cu2O nanocubes through a simple physical mixing strategy to investigate how the polymer structure regulates CO2 reduction behavior on an identical Cu2O platform. Among these modifiers, Cu2O@PVP/C exhibited the best C2+ performance, achieving a C2+ faradaic efficiency of nearly 60% and an ethylene partial current density of 70 mA cm−2 at −1.4 V vs. RHE. CO2 adsorption measurements and molecular dynamics simulations reveal that the PVP interfacial layer promotes local CO2 enrichment near the catalyst surface while maintaining CO2-accessible pathways. XPS/Cu LMM analysis and DFT calculations further indicate that PVP modulates the electronic environment of surface Cu sites and stabilizes key *CHO and *COCHO intermediates, thereby facilitating C–C coupling. This work demonstrates that polymer-mediated CO2RR performance is governed not only by hydrophilicity or hydrophobicity, but also by the synergistic regulation of local reactant distribution and surface electronic structure. These findings provide molecular-level guidance for designing polymer-modified Cu catalysts for selective C2+ electrosynthesis.