As potassium-bearing shale is still being developed as a potential alternative to potash, the first step to improve its utilisation is to reduce its particle size. This paper explores whether roasting pre-cracked potassium-bearing shale can improve the quality of ultra-fine crushing products. By analysing the particle size distribution and the fractal dimension of the particle size distribution, the results for 1 h and 2 h roasting pre-cracking experiments were found to be contradictory. AHP-fuzzy comprehensive evaluation of the three indicators of product quality and quantity was used, resulting in a unique indicator. Roasting pre-cracking for 2 h was found to have a facilitating effect, with the average of the three fuzzy comprehensive evaluation values increasing from 0.71 to 0.78. The great difference in cost outlay suggests that the technique is not suitable for industrial applications. Subsequently, two groups of microwave pretreatment experiments were carried out but led to unsatisfactory results in which microwave pretreatment was not conducive to the ultrafine grinding of potassium-bearing shale.