By using fractal theory, the analysis of the particle size distribution of the slacking products of red beds soft rock in nature environments shows that the slack process tends to stagnate when the fractal dimension value reaches the interval of 2.6~2.7. After analyzing the crushing ability of hydraulic breaking hammer and sheep-foot roller on red beds soft rock, the mechanical crushing technology to aim at eliminating the slacking properties of red beds soft rock was proposed. The core of this technology is “milling and compressing” action, which is based on the unique iteration character in the process of creating a fractal figure. On-site experiments on the technology were conducted subsequently on Liu-Li Expressway. Calculation results of the fractal dimension value on the particle size distribution data of soft rock material show that 2 times of “milling and compaction” action can crush the red beds soft rock to the extent that its fractal dimension value can reach the interval of 2.6~2.7. The results verified the mechanical crushing technology developed based on the fractal iteration character, which could eliminate the slacking properties of red beds soft rock. The crushing technology has been applied in the expressway construction process and can extend the application of red beds soft rock material from the lower embankment to the upper embankment.