Abstract: The vacuum fish pump is an important tool for catching and conveying fish in aquaculture. In order to research the relationship among the pumping pressure, suction range and pipe inlet velocity of the vacuum fish pump, five different suction range geometric models of the vacuum fish pump were established. The transient Volume of Fluid method was used to capture the changes of gas-liquid two-phase flow at the water gas interface under the influence of different parameters. The numerical results are displayed: under the same pumping pressure, the inlet velocity of pipes with different suction ranges increases rapidly within 0.5 s, and then the fluctuation decreases, the average velocity deviation at the inlet of the pipeline is less than 3.4%, indicating that the average velocity at the inlet of the pipe is hardly affected by the suction head. After the water in the pipeline is pumped to the fish collecting tank, it is filled with a large amount of foam gas-liquid mixture composed of water and air mass. At t=8 s, all the fish bins with different suction ranges have been filled with water. The critical pumping pressure corresponding to suction range of 2, 3, 4, 5 and 6 m is-13,-14,-16,-20 and-25 kPa respectively. The relationship between suction range and critical extraction pressure can be fitted as a polynomial; the maximum suction negative pressure required by the same vacuum fish pump under any suction range can be calculated.