In this work, we modified NaY zeolite (Si/Al = 5) with NaOH solutions of different concentrations followed by ion exchange with NH4NO3 to the H form of the zeolite. Treated NaY was used as a catalyst support for the preparation of CuY for diethyl carbonate (DEC) synthesis through the oxidative carbonylation of ethanol. The textural and acidic properties of NaY and the catalytic performance of the corresponding CuY materials were investigated. Compared with the untreated sample, CuY catalysts using modified NaY samples as supports exhibited higher conversions of ethanol and similar selectivities to DEC. Inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), N-2 adsorption, Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM) were used to explore the origin of the improvement in activity. The experimental results showed that alkaline treatment induced defects in the zeolite framework and greatly promoted dealumination through ion exchange assisted by microwave radiation, which caused the generation of meso- and macropores in zeolite Y and contributed to the catalytic performance. Furthermore, the increased amount of hydroxyl species in supercages and extraframework aluminum species resulted in an increase in the number of Cu active sites and further DEC production.