The first-order critical speed of a rotor is obtained by experiment on a rotor experimental platform,and the result is compared with the predicted one obtained by Prohl technique.A data acquisition program is made by LabVIEW in order to gather signals of the rotor vibration and display signals in different forms.When the amplitude and phase of the rotor suddenly change,the corresponding speed is the critical speed.According to Prohl method,a program is written by VB in order to get the predicted value of the rotor critical speeds.The result shows that the tested data are almost consistent with the predicted ones.