In the process of manufacturing ultra-large mirrors,there is very limited space beneath the mirror′s back,the machine platform has limited carrying capacity,so the polishing support system (PSS) should be structured simply.Also as the mirror is suffering from fabricating load and polishing powder which is very“dirty”spreads everywhere,PPS should not be sensitive to polishing load and its working environment.Moreover,when one wants to speed up the polishing through online testing,PPS should be adjustable and stable enough.An equalforce hydrostatic support system is designed,afterward the equal-force performance and static stiffness of PSS′s single support structure are tested,then the print-through effect is predicted,finally the corresponding control method is proposed and PPS is integrated with (GUI) operation.Applied to the polishing of a 2 m SiC mirror,PPS restricts the magnitude of print-through effect to 13.1 nm≈l/48,which is considered stiff enough.And PPS achieves an angle adjusting region of 0.34″~0.48° and a ±5 mm motion along Z axis for the mirror.The angle adjustment makes the corresponding XY-plane motion of the curvature center range from 50 mm to 10 mm,which is close to the size of charge couple device (CCD)′s basic unit,showing it suitable for mirror adjustment during vertical testing.The proposed hydrostatic support system has a good adaptability to 2~4 m class mirrors,which are in great demand.