<p>Internal defect is a general problem in cross wedge rolling, which usually diminishes mechanical properties and even leads to the failure of rolled workpieces. In this study, variation of characteristics (stress state, strain path, etc.) in rolled workpieces during deformation was investigated through numerical simulation. Then, microstructural evolution of internal defects was clarified by quasi-in-situ experiments. Finally, process parameter intervals forming rolled workpieces with internal defect-free and good mechanical properties were confirmed. Results show that rolled workpieces with good surface quality can be produced although they experience complex strain paths and stress states during deformation. Further, quasi-in-situ experiments revealed that evolution process of internal defects. Namely, defect nucleates at interface between inclusion and matrix, and grows into a micro-pore. As section shrinkage increases, micro-pores gradually expand and coalesce, forming larger micro-holes and potentially leading to macro-cracks. Among them, propagation process is accelerated by fine carbide particles served as expansion channels. In addition, rolled workpieces with good internal and external quality can be formed at a heating temperature of 970–1 020 °C and a rolling velocity of 400 mm/s. Specially, area proportion of defects was counted quantitatively to characterize damage degree. At a fixed velocity of 400 mm/s, as temperature increased from 950 °C to 1 050 °C, area proportion changed from 1.4% (950 °C) to 1.1% (1 000 °C) and 1.3% (1 050 °C). When temperature is settled at 1 000 °C, changes in velocity (300–500 mm/s) can also cause similar trends in area fraction variations. Consequently, rolled workpiece obtained through process optimization can provide a 5.1% increase in tensile strength while maintaining hardness of central region.</p>