<p>At present, wire arc additive manufacturing (WAAM) technology is widely used in the forming of various alloy materials. However, there is still limited research on 2xxx Al-Cu alloys formed by WAAM, such as UNS A92319 aluminum alloy (2319 aluminum alloy). It is important to enhance the mechanical properties of WAAM 2319 aluminum alloy for further industrial demand by controlling phase precipitation. In this study, the changes in microstructure, phase, and mechanical properties of different areas along the building direction before and after heat treatment were comprehensively investigated. The as-built WAAM 2319 aluminum alloy exhibits the decrease in grain size, width of coarse eutectic Al-Cu phase, and number of needle-like Si phases with decreasing deposition layer height, while its mechanical properties increase accordingly. Solution treatment completely dissolved the needle-like Si phase and eliminated the differences in microstructure and mechanical properties in different areas. However, the coarsened eutectic Al-Cu phase results in poor strength of ST WAAM 2319 aluminum alloy. Aging treatment can decompose coarse eutectic Al-Cu phase and precipitate nano Si phase, which greatly improves the strength of SAT WAAM 2319 aluminum alloy.</p>