An ultra-precision machining system for smaller lens mould was developed. It is composed of an ultra-precision machine, which uses linear guide and linear servo motor for the X and Z tables, On-Machine Measurement (OMM) system and ultra-precision CAM system. It combines diamond turning, grinding and OMM functions in one system, realising highly efficient and ultra-precision machining of lens mould by the compensation function based on OMM results. Experimental results demonstrated that ultra-precision and high-efficiency machining of small lens mould can be achieved using the developed system.