Large reflective aspherical optical components with high-precision free-form surfaces and a maximum length exceeding 100 mm are widely used for optical parts of automobile Head-Up Display (HUD) systems, focusing devices for X-ray or neutron beams, etc. On-machine measurement on ultrahigh precision machine tools is an effective method for high precision and rapid manufacturing of large free-form optics. An on-machine surface profile measurement system has been developed for high-accuracy surface profile measurement of free-form optics using a laser auto-focus probe with 1 nm resolution linear scale and high-speed displacement acquisition system. The system enables high-speed and damage-less surface measurement of fabricated optical surfaces made of aluminum or other soft metal materials.