Abstract: Heavy medium vessel (HMV) is nowadays a primary power coal washing equipment. With the W26F60 version currently used at Hongliu Coal Preparation Plant as the object of study, the paper makes a two-dimensional numerical simulation of the flow field inside the bath based on the actual bath dimensions and measured parameters by using the software FLUENT, as well as an analysis of the factors causing the occurrence of some common troubles, such as the operation of the reject scraper conveyor under unbalanced load. Study result shows that: an ideal flow field distribution in the separating bath can be expected when the total flow volume of horizontal current and that of the upward flow are controlled in a ratio ranging from 4∶1～9∶1; The unbalanced loading of the reject scraper conveyor and entrainment of coal into rejects are attributed to the fact that the large pieces of rejects are directly washed down to the bottom of the bath by the obliquely downward flow of the “horizontal current” from near the side wall where no upward flow is available; and under the precondition that no adverse effect is produced on flow field distribution, the fitting of an grid-type deflector plate in the bath can enable the large pieces of rejects to be guided to the central part of the scraper conveyor′s trough, allowing the washing equipment to operate with an ideal performance.