The change of the number of M23C6 particles intercepting mobile dislocations by creep of high‐chromium creep resistant steel is deduced. With tempering at 800 °C, the number of intercept particles decreases slower than the total number of particles. The dissolution velocity of particles is greater by smaller particles. By tempering at 550 °C and higher, the dissolution of small particles increases the intercept particles spacing and the creep rate for about 1 order of magnitude stronger than the increase of average particles size. M23C6 particles size, number and dissolution velocity were deduced for tempering of a X20 steel at 800 to 550 °C. The dissolution of small particles increases the particle spacing for above one order of magnitude more than particles coarsening. By creep tests above 550 °C, particles spacing and creep rate are increased significantly by dissolution of small particles.