Abstract: Along with the development of the mining technology, the content of fines coal in raw coal is becoming more and more，and the separation results of coarse slime would directly affect the quality of clean coal. To reduce the ash of coarse fines coal and improve recovery rate of clean coal, Zhangjiakou coal preparation plant used CSS separator to replace spiral separator, and made technology transformation. This paper introduces the thought and reforming scheme and concrete implement process of system transformation. By comparing the selected effect, and combining the reality of produce, this paper considers that choosing CSS separator to make technology transformation of coarse slime separation system is very successful.