Abstract: The difference between the measured diameter and the target diameter on different height sections of the forming part was taken as the criterion of flanging accuracy. The effect of process parameters on flanging accuracy of 5182-O aluminium alloy sheet in hole incremental flanging with three-pass round holes was studied. The results show that the initial forming angle has a significant influence on the precision of the flanging part. It is advisable to adopt a smaller initial forming angle to ensure sufficient deformation in the second and third passes of forming, so that the deviation between the measured diameter and the target diameter of the forming part is gradually reduced after each pass of forming, and the hole incremental flanging parts with higher accuracy can be obtained. The depth increment has a great influence on the dimension deviation of formed parts. When the depth increment of the tool head is greater than a certain value, the contact area between the tool head and the sheet metal is completely located on the side of the undeformed sheet metal at the boundary between the deformed zone and the undeformed zone. When the tool head continues to progressively extrude the sheet metal, the extrusion deformation area drives the deformed zone to continue to deform, causing the size of deformed zone to increase. The size of the final part becomes larger, and even the positive deviation of the size of the formed part occurs.