Purpose <p>Water-lubricated hydrodynamic spiral-grooved bearings enable motorized spindles to achieve very high rotational speeds. Nevertheless, because water provides substantially lower viscous damping than oil, maintaining the dynamic stability of spindles supported by these bearings remains a critical challenge that demands immediate attention.</p> Methods <p>A five-degree-of-freedom nonlinear rotor–bearing model was established for the proposed motorized spindle by coupling the rotor dynamic equations with the equivalent Reynolds equations of the hydrodynamic spiral-grooved bearings. The model was employed to evaluate spindle stability and cutting-force responses. A prototype spindle and a dedicated test rig were fabricated to characterize the system’s dynamic behavior experimentally. Finally, the dynamic stability of the new spindle was compared with that of a reference spindle with plain journal bearings (PJBs).</p> Results <p>Numerical simulations show that the logarithmic decrement of the proposed motorized spindle remains positive throughout the entire speed range up to 30 000 rpm, confirming dynamic stability. The calculated cutting-force response exhibits a strictly monotonic decay, indicative of a well-damped transient. Compared with the reference spindle with conventional plain journal bearings, the water-lubricated, hydrodynamic spiral-grooved bearing spindle demonstrates markedly superior stability.</p> Conclusions <p>The results demonstrate that the motorized spindle with water-lubricated hydrodynamic spiral-grooved bearings exhibits outstanding dynamic stability and superior impact resistance.</p>