Abstract: In this paper, the relationship between stress and strain on the surface of brittle or quasi brittle materials is obtained by the high temperature Hertzian indentation method. According to the analysis of the indentation stress strain curve, the indentation modulus, the shear modulus and the hardness of the material can be determined and the deformation properties of the cement clinker are compared. Under the high temperature heat treatment of different temperatures (25 ^\circ\!C\sim 1400 ^\circ\!C), the stress relaxation of the Hertzian indentation is observed. When the load peak value is 100 N, the load relaxation of the cement clinker is more obvious with the increase of the temperature. With the temperature increasing from 500 ^\circ\!C to 1400 ^\circ\!C, the load relaxation is very significant, especially at 1200 ^\circ\!C. For the cement clinker samples within the C3S decomposition and the partial liquid phase, the stress relaxation is observed, most obviously at 1275 ^\circ\!C, the clinker softened, and the relaxation load is 0 N. So 1275 ^\circ\!C is the brittle ductile transition temperature of the clinker. The brittle plastic transition temperature of the cement clinker during the two heating processes can be determined by the high temperature Hertzian indentation relaxation test for the cement clinker. The temperature range for the sharp change of the elastic modulus and the compressive strength of the clinker can be determined. To study the mechanical behavior and the mechanical properties of the cement clinker at different temperatures, new ways to improve the grinding efficiency should be explored.