Abstract: To determine the values of two constants C and m in Paris equation, generally a lot of parameters are to be determined or the data resulting from complex tests are to be analyzed. A new way is proposed to solve the tedious problem by the inversion of compressive strength of concrete so as to obtain the total area of initial cracks and pores. Then, the stress intensity factor is converted into the stress the specimens are undergoing according to the expression of stress intensity factor of circular crack in fracture mechanics. In such a way the values of C and m are given by the data resulting from the uniaxial tensile fatigue tests of plain concrete. The analysis shows that the values of relevant parameters change greatly with the stress level, and the value of C changes in several orders of magnitude even though the value of m changes in the same order of magnitude. It's found that the values of relevant parameters are comparatively reliable if the max stress level is equal to 0.7.