This paper made an experimental investigation of cage instability in respect to cage pocket designs, ball-pocket clearances, and flow rate in cryogenic environment. Test bearing bore size is 70 mm deep groove ball bearing. Cage pocket designs are circular and elliptical, and ball-pocket clearances are 0.6, 1.2, 1.8 mm. Test is operating at 6000 rpm during 1500 s in liquid nitrogen. As a several criterions of wear and stability for cryogenic ball bearing, we measured a friction coefficient of bearing and sound vibration FFT were measured and analyzed to predict failure mechanism of bearing elements. From these results, predicted and diagnosed with sound properties of cage, inner/outer race and balls. These works will be assessed more stable with optimum ball-pocket clearance and elliptical pocket design bearing in sufficient coolant.