Abstract: Based on the theory of CFD analysis method, the internal flow field of the negative pressure dust-catch device in the coal-mouth of fully-mechanized support was simulated, and the influence of nozzle water pressure on flow field vacuum degree was analyzed. The simulation results showed that the fundamental reason that the device could catch dust was that there was large relative vacuum degree in the connecting pipes of dust-catch hood; the ideal water pressure was 4MPa, the length of the dust-catch hood should be short and the installation location was close to the dust producing field.