In order to reduce the vibration of the ground rotor tester， dynamic balance of the rotor need to be carried out. In this paper， a calculation model of rotor unbalance is established based on all-phase fast Fourier transform （FFT）， and an unbalance test system is built on the ground rotor tester. The test shows that the rotor unbalance response can be accurately measured and analyzed when the speed is higher than 1kr/min. Finally， the ground rotor tester is dynamically balanced on site， and the results show that the unbalance vibration of the rotor can be reduced by 77.3% with a single time under light test conditions， in that the three-circle method could not calculate the balancing scheme， which proves the effectiveness and reliability of the unbalance calculation model， and the model can be applied to the field dynamic balance of other rotor machines.