By low temperature gas multi-component thermochemical treatment, C, N, and O three elements are simultaneously infiltrated into the surface of steel 20, forming a dense, homogeneous, 50μm penetrating layer and about 150μm transition layer. X ray diffractometer and sweep electron microscope are used to measure the phase components and surface morphology. The results show that the penetrating layer is mainly composed of oxides and nitrides. After gas multi-component thermochemical treatment, the hardness on the surface penetrating layer of steel 20 may reach up to over 800HV, 3 times more than that of the original material; the hardness of transition layer is about 300HV, also higher than that of the original material. Within the temperature range of the test, the surface hardness increases with the rise of heating temperature, and the thickness of penetrating layer also increases with the rise of temperature. The tribological experiment shows that after multi-component thermochemical treatment, the lowest friction factor of steel 20 is 0.25, while the friction factor of the original material is 0.5; the wear resistance was improved.