Abstract: This paper analyzes the difference between the design coal sample and the actual coal sample in Qinglongsi coal preparation plant, and points out the existing problems of the coal washing process. The original design of the process is preparation of sized raw coal. The raw coal is firstly sized by the dry screening, then mixed and the smalls are removed by the lump coal stroke with wet screening, and finally the smalls are preparation by dense medium separation after the wet screening, which causes a series kinds of problems due to the serious coal mud conversion, which can not be realized in the current production. It can be completely realized by preparing of sized raw coal and shortening the overwater time of the raw coal, at the same time, it can bring good economic benefits for the coal preparation plant.