The influence of different scratching speed of scratches on the critical state of brittle-plastic transition of single crystal germanium was studied based on the nano-scratch experiments, which were carried out on single crystal germanium (100) (110) (111) crystal surface by using a nano indentation instrument. Atomic force microscope was applied to observe the material surface. The results show that the plastic removal region of single crystal germanium will increase with the scratching speed raises. Nevertheless, the plastic removal region of single crystal germanium may decrease if the speed of scratches is too large. Furthermore, the influencing rules of cutting speed on the critical state of brittle to plastic transition of single crystal germanium in the ultra-precision machining process is predicted, which provides the data support for the ultra-precision machining of single-crystal germanium parts.