Abstract: As the plant′s middling product is rather low in ash, a study is made on the technical process for rewashing of the middling product of the heavy medum separation system after being crushed. For attaining an optimum liberation effect, test is made on crushing of the product into 3 different sizes for analysis of its liberation characteristics and determining the appropriate crushing size. The effect of the separation of the crushed middlings is predicted based on float-and-sink analysis data and result of batch flotation test. Finally, an optimal middlings rewashing process is proposed.