Under the action of relatively low stresses and high temperatures, metallic materials become brittle and fractured with a small value of residual deformations. This problem is known as a problem of thermal brittleness of metals. To solve this challenge in the mechanics of materials the damage conception was introduced. To describe the brittle region of the experimental long-term strength curve, the system of simple kinetic equations for the damage parameter and creep deformation was proposed, and the long-term strength criterion was formulated. In this work, we propose to determine the damage parameter changes according to the experimental high-temperature creep curves. Only one kinetic equation for creep rate for compressible medium, recorded using the damage parameter is formulated. From this equation, the damage parameter is determined, depending on the creep rate and the creep deformation. Similarly, the value of the damage parameter is determined according to the Rabotnov solution. To describe the experimental creep curves various empirical dependences in the form of power, exponential, and mixed functions are used. Theoretical damage curves are plotted. The corresponding theoretical long-term strength curves are constructed.