<p>The spinning bending process (SBP) of the big-tapered profiled ring disk is a complex, dynamic and incremental forming process. How to successfully establish the SBP and realize the stable and precise forming of ring disk by reasonable process design is a crucial issue urgently to be solved. To solve this, this work studies the stable forming condition of the SBP. To reduce the dynamic contact and collisions between ring disk and rolls and improve process stability, the constant diameter reduction velocity condition (CDRVC) of ring disk is proposed as the process design goal. A mathematical model of stable forming condition for the SBP is established by theoretical analysis, which not only describes the mathematical correlations among the key process parameters but also gives their reasonable ranges. The application of this model is detailedly expounded by a specific case study. To verify the stable forming condition, an instantaneous passive compliance support method for guide rolls is proposed, based on which a 3D FE model of the SBP that can realize accurate motion control of guide rolls is established under ABAQUS/Explicit platform. The simulative results indicate the process parameters designed by the stable forming condition can ensure the successful establishment of the SBP and effectively improve the whole process stability. Overall considering the geometric accuracy, rotational condition, process stability and processing efficiency, it is recommended to select the diameter reduction velocity of ring disk near the median of the reasonable range determined by the stable forming condition.</p>