With the continuous improvement of the degree of mechanized mining in coal mines, the content of pulverized coal in raw coal increases, which increases the load on the flotation system of coal preparation plants. In this study, the process problems of desliming and ash reduction and effective recovery of coarse slime in coarse slime system were analyzed, and the process flow was optimized. By comparing the different installation angles, different process parameters and screening effect of arc sieve, the optimum scheme was selected. The flotation efficiency of the improved coal washing plant was increased by about 15 %, and the flotation cost per ton of coal was reduced by about 12 %. The improvement effectively reduced the loss of clean coal, ensured the maximization of clean coal quality and yield, reduced production costs, and improved economic efficiency.