Abstract: To address the issues of high ash content, excessive moisture, and significant quality fluctuations in fine clean coal, the Guobei Coal Preparation Plant analyzed the particle size, density, and moisture distribution characteristics of fine clean coal using small-scale screening tests, float-and-sink tests, and Low-Field Nuclear Magnetic Resonance (LF-NMR) moisture detection technology. Semi-industrial separation tests were conducted using the WHS-150 large-cone-angle water-only cyclone to establish a collaborative process of water-only cyclone separation and classification desliming. Furthermore, the on-site coarse slime treatment flow was optimized, and material balance calculations were performed. The results indicate that the ash content of fine clean coal increases significantly as particle size decreases, with the ash content of the < 0.045 mm fraction reaching as high as 32.88%. Consequently, it is difficult to control the ash content below 11.00% by relying solely on classification desliming. The water-only cyclone effectively separates coarse coal slime, reducing the overflow ash content to 10.19%, while the underflow ash content reaches a maximum of 37.51%, allowing it to be directly utilized as middlings. The optimized process enables the ash and moisture content of fine clean coal to meet product quality requirements. Combining separation with desliming can significantly reduce the ash and moisture of fine clean coal, improve product quality, and enhance the separation efficiency of the coarse coal slime system.