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Single crystal germanium is an important infrared optical material, which is widely used in defense industry, microelectronics, and other fields. It is extremely difficult to achieve the required surface quality by conventional processing methods due to its hardness and brittleness. Practically, single-point diamond tool is used for micro-cutting. During the micro-cutting process of single crystal germanium, the change of cutting temperature leads to increased tool wear and material surface hardening, which results in poor surface quality and also reduces processing accuracy. Therefore, analyzing the micro-cutting temperature distribution of single crystal germanium has become the key to better understanding its heat transfer mechanism and for improving product quality and efficiency. Aiming to analyze heat transfer mechanism of single crystal germanium micro-cutting, the moving heat source method was used. It establishes the theoretical model with temperature rise during micro-cutting of single crystal germanium under the action of the heat source of the shear slip surface and the friction heat source of the rake face and the chip, respectively. The maximum cutting temperature of germanium at three cutting speeds, and the model was verified with the cutting temperature of homogeneous hard and brittle material single crystal silicon. Through a single-point diamond turning experiment, an infrared thermal imager was used to measure the temperature of the single crystal germanium micro-cutting process online. When experimental measurement results and the model calculation results are compared, it revealed that the maximum cutting temperature of single crystal germanium has displayed same trend under different cutting speeds, which is that the cutting temperature is directly proportional to the cutting speed. The relative error is found to be between 2.56% and 6.64%. The relative error of the maximum cutting temperature is 3.84%. The model can accurately predict the temperature field of single crystal germanium and also for similar hard and brittle materials, providing further theoretical support for analyzing its thermal effects.