Abstract: The invention provides a method for predicting the performance of a centrifugal pump with a balance mechanism comprising the steps of assuming leakage amounts in the back of an impeller and a thrust balance mechanism to calculate a flow-rate of the impeller for monitoring a leakage amount of a front and a back of the impeller, calculating a leakage amount in the thrust balance mechanism for judging whether or not a result of the calculation converges, to a set value. If the result does not converge, repeating the steps from the analysis of the flow in the thrust balance mechanism to the calculation of the leakage amount in the thrust balance mechanism. If the result converges, calculating a leakage amount in the pump. If a result of the calculation does not converge, repeating the steps from the calculation of the flow-rate in the impeller until the convergence.