The stability and the leakage performance of turbo pump unit seals supported by elastic-ring ball bearings are Investigated for the Improvement of onset speed of instability(OSI). The numerical analysis of floating ring seal in consistence with its geometry and operating conditions is executed with detailed comparison of various seal types. The results show that the floating ring seal has superior performance in terms of rotordynamic salability compared to the ocher type seals while it shows slightly inferior leakage performance. To Improve the leakage performance. floating ring seal could be combined with hole Pattern damper or labyrinth seal surface.