Radial under-race lubrication technology offers an innovative solution for high-speed bearings in aero-engines, aiming to minimize oil flow rate and engine power loss. This study, through experimental and CFD simulation methods, evaluates the entire operational process of radial under-race lubrication - capturing, delivering, and expelling oil. It elucidates the mechanisms through which oil supply parameters, particularly the orifice diameter, affect both oil capture efficiency and flow rate, while identifying the optimal range of orifice diameters under various oil supply conditions. An improper orifice diameter can reduce oil capture efficiency by up to 45 %. In engineering applications, achieving a higher oil capture flow rate may necessitate sacrificing a portion of oil capture efficiency. Optimized oil capture efficiency consistently exceeds 80 %, with a significant improvement of over 20 %. Owing to the competitive relationship between the relative error of oil supply and capture efficiency, it is necessary to reconcile these factors to achieve optimal performance.