Abstract: The problem with the operation of the plant′s middlings rewashing system currently used is the wide fluctuation of percentage of cleaned coal in middlings which can go up to 30% with the ash of the middlings being in a range of 30%～35%, causing a great loss of cleaned coal. To cope with this situation, work is made on optimization of the heavy medium washing process to enable it to make high-precision rewashing of the middlings product of the primary washing system. In the optimized washing system, the 2-stage 3-product process is changed to a 2-stage 4-product one, and the pressure-fed 3-product H. M. cyclone is employed to replace the 2-product version previously used. After optimization the clean coal with an ash of 10%～12% can be effectively recovered. Field application of the renovated washing system shows that the total yield of clean coal is noticeably increased, and the 3^# clean coal product has a final ash of 11% with a rise of yield by 1.12 percentage points, creating a remarkable economic result.