Three-layer solid elements and shell elements were used for numerically simulating the incremental forming process of asymmetric part (figure-eight part) to research the thickness changes and the stress states in different regions of sheet, as wall as the proportion and evolution history of strain components in each region during the forming process, and the two characteristic sections of middle section and corner section for part were compared. The results show that the incremental forming process has local deformation characteristics, and the strain value in the area near the tool head increases sharply while the strain value in the far away the tool head slowly increases and gradually stabilizes. Although the forming angle is the same, the thickness reduction on the middle section of figure-eight part after forming is more serious than that on the corner section, the proportions of the normal strain component on the middle and corner sections are approximately the same, the former has a larger proportion for shearing strain ε12 and the latter has a large portion for shearing strain ε23 in yz plane which shows that the ε12 is the main cause of more serious thickness reduction on the middle section. Thus, the forming process is a combination of stretching, shearing and bending effects, and the tensile effect and the bending effect are superimposed on each other. Meanwhile, the tensile effect has the most significant effect on the forming process, and the sine law cannot be fully applied to the prediction of the thickness for asymmetric part.