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Incremental sheet forming (ISF) is a new promising manufacturing technology with high potential to shape complex three-dimensional parts by using a relative small tool. However, ISF is presently limited due to non-uniform thickness distribution of formed parts, especially excessive thinning on severely sloped regions. This typically leads to fracture and hence limits process formability. This paper aims to tackle this issue by developing appropriate tool path strategies for multi-pass deformation design in ISF. More specifically, two more complex shapes are designed to validate the proposed multi-pass deformation design methodology by finite element simulations and experiments. The interactions of different tool path strategies on material thinning of the final part are evaluated in terms of process formability and thickness strain distribution given the same multi-pass design. Furthermore, the movement of material points is traced to explain the material flow mechanism in multi-pass forming compared to single-pass forming. It is concluded that both deformation passes (intermediate shapes) and tool path generation strategies would influence the thickness strain distribution as well as process formability. Appropriate tool paths should be devised to further reduce material thinning and improve the process formability by taking the geometrical features of the designed part into account. Additionally, the proposed multi-pass deformation design enables sufficient material to flow into the deformed region from the outside region so as to allow a compressive deformation state to develop and steeper shapes to be formed.