Surface quality of optical glass is crucial for application in high precision products. This paper aim to investigate the surface roughness improvement and the limit surface roughness of the BK7 optical glass for mirror-like surface finish. Due to the brittleness of workpiece, lapping pressure need to be controlled diligently to prevent crack and brittle fracture from occurring. At first, the new lapping tool is installed on the collect chuck of the CNC milling machine and lapping is performed by the table movement in X and Y direction by NC control. Then, suitable lapping parameters are carefully selected for ductile mode machining in mirror-like finishing process. According to results, the mirror-like surface is achievd with proposed lapping method especially in low lapping pressure of 25MPa
