Nowadays, thin-walled tube bending at small bending ratios is a production process widely used in advanced industries. This research has been carried out to obtain the smallest bending ratio, and maximum applicable internal pressure in Hydro-rotary draw bending of thin-walled AA8112 alloy tube using necking criterion. To accomplish the objective, equivalent plastic strain of extrados critical region has been selected for necking criterion. The results showed that the selected necking criterion would be able to successfully determine the onset of rupture in bending. In order to validate FE simulation, the effects of bending ratio and internal pressure on defects, such as cross-section ovality and thickness changing, have also been investigated through simulation in ABAQUS software and experiments.