Operating conditions of the floating impeller was simulated with special equipment, and the fore-and-aft pressure of the back seal ring on the impeller was measured directly. The test curves of fore-and-aft pressure of the back seal ring and pump head were obtained. Thus the fluid leakage curve of the balance cavity of the floating impeller was got. The study solved the calculation problem of chamber pressure and leakage calculation in balance cavity of the floating impeller.