Wire-arc directed energy deposition is promising for manufacturing ultra-high-strength Al-Zn-Mg-Cu alloy components. However, the undesired microstructure and performance of as-deposited alloys make the heat treatment a mandatory post-process, which still lacks systematic investigation. This work aims to establish a comprehensive understanding of it. An interplay between second-phase dissolution and defect formation in the single-stage solution of as-deposited Al-Zn-Mg-Cu alloy was found: as solution temperatures increase, the equilibrium proportion of residual phases decreases, but the proportion of pore defects increases significantly. Based on a systematic full-factor solution test, a 430°C/4 h + 450°C/4 h step solution process was proposed, which suppressed the pore defects by about 54.8% while keeping the effect of the residual phase dissolution unchanged. After the step solution and artificial aging, the average yield strength of the alloy reached 475 MPa, and the elongation reached 6.5%, showing 201.6% and 85.7% improvement compared with the as-deposited state, respectively.