Wire arc additive manufacturing (WAAM) has become a promising metal 3D printing technology due to its high efficiency and low cost. Process planning is a critical step in WAAM that influences the process output attributes in terms of surface accuracy, deposition rate and material utilization. Generally, traditional methods are only able to satisfy the variation of bead width, regardless of the control on bead height, which may not obtain the optimal process output attributes. To solve this issue, a unit block-based process planning strategy is proposed, which aims at slicing the complex component into parallel layers with uneven layer thickness. A unit block is defined as the deposited block per unit time, whose dimensions can be controlled by varying the process parameters. Once the part’s 3D model as well as the optimization criteria is given, the best unit blocks that fit this 3D model are determined and so are the process parameters. This enables to generate varying process parameters subjected to the part’s geometrical features and ultimately the optimal process output that balances surface accuracy, deposition rate and material utilization. The case study for an aerospace component proves that the proposed method is capable of improving the surface waviness by 46.2%, effective deposition rate by 65.6% and as well as the materials utilization by 4.2% with block unit width of 6mm.