Abstract: Abstract: In the design of a centrifugal pump, the double seal ring impeller with the balance hole is the main methods of balancing axial thrust. The cover force produced by the pressure difference in the balance cavity region was the main part of axial thrust. A study on the calculation method of fluid pressure of the balance cavity in the impeller has important significance for the accurate calculation of the axial thrust. In order to solve the fluid pressure calculation of the balance cavity in the impeller, the two dimensionless characteristic parameters about specific areaand pressure coefficientwere introduced. Under the condition of the fluid leakage in the balance hole and the back seal ring clearance at the impeller was equal, a calculation model of fluid pressure in the balance cavity was derived. The dimensionless curve of the calculation model was, and an undetermined coefficient a and b in calculation method was introduced. For the 3BA-6 pump, under the condition of the different diameter of the balance hole, the theoretical dimensionless curves of the fluid pressure in the balance cavity at design point were obtained. To illustrate the problem, under the condition of the same pump structure, a verification experiment by taking the same diameter of balance hole as the calculation was conducted. The fluid pressure of the back seal ring outlet and impeller inlet at the design point was measured, so the experiment dimensionless curve was obtained. Research showed that, the experiment dimensionless curve and the theoretical dimensionless curve on the fluid pressure in the balance cavity at the design point were coincident, and the test curve above the theoretical curve, but when 0.5, was maximum between the experiment dimensionless curve and the theoretical dimensionless curve, the maximum absolute error was 0.049. The result proved that the calculation model of fluid pressure in the balance cavity was correct and feasible. For a centrifugal pump of double seal ring impeller with a balance hole, the specific expressions on the calculation model of fluid pressure in the balance cavity by calculating was obtained. Furthermore, the pressure difference of the two sides of the impeller back cover and the cover force produced by the pressure difference in balance cavity region can be calculated.