In order to solve the problem of ion beam figuring, the design and performance analysis of ultra-precision ion beam polishing tool was studied. The research on ion beam polishing tools design method, the structure design of a 3-grid focused ion optics system and the performance analysis of ion beam was covered. Based on the theoretic calculation and computer simulation, a focused ion optical system was developed. In this ion optical system, an integrated plasma bridge neutralizer was designed to fully neutralize ion beam extracted from ion source. Finally, a 150mm flat optics was figured by two designed focused ion optical systems with 15mm and 10mm output diameter. Figuring result shows that the contour error of this flat is decreased from 15.58nm RMS to 0.79nm RMS. Result further demonstrates that the designed ion beam polishing tool is very efficient to optical ion beam figuring.