Concave aspheric surface with small radius is difficult to be fabricated by most of existing technologies for optical manufacture. Ultrasonic- magnetorheological compound finishing (UMC finishing) is a new technology for the ultra-precision machining of concave aspheric surface with small radius and freeform surface. The principle and experimental deviece used in UMC finishing are introduced. Main technological parameters in UMC finishing include the magnetic flux density, the gap between the polishing tool head and the workpiece, the rotational speed of polishing tool head and so on. The technology experiment of UMC finishing for optical glass K9 is conducted, and the influence of main technological parameters on the material removal rate has been studied by analysis of experimental results. The analysis of removal profile curve of UMC finishing spots prove that the material removal function of UMC finishing meet the surface error convergence requiement in computer control precise optical surface machining. The part surfaces after UMC finishing are measured by an Atomic Force Microscopy (AFM), and the surface roughness Ra is 1.591 nm after polishing for 10 min. It is demonstrated that the polishing capability of the technology is excellent.