The Berkovich indenter was selected to perform an varied load nano-scratching experiment for monocrystalline Germanium by using nano indentation test. The surface morphology of the groove was observed by SEM, which was found that there are three regimes in nano scratching process, i.e. the ductile regime, the brittle-ductile transition regime and the brittle regime, and the mechanical characteristics at each regime was analyzed. According to the theory of fracture mechanics, the first drop of tangential force was taken as the occurrence point of brittle-ductile transition, thus the critical load and critical depth for monocrystalline Germanium were obtained, and the crack generation and propagation process were also analyzed. Non-linear fitting method was used to figure out relationship between normal force, tangential force, friction factor and scratch depth respectively during nano-scratching process, the calculation results of the correlation coefficient show that there is a strong correlation between scratch force and scratch depth. Based on the Hertzian contact theory, the critical elastic-plastic transition depth during the scratch process for monocrystalline Germanium is calculated, and the value is 1.2 nm. Based on the critical load of brittle-ductile transition, An equation for characterizing the phenomenon is established, the results show that the transition depth is 561 nm. Therefore, a quantitative method for distinguishing different regimes of monocrystalline Germanium is established.