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When measurement rotating speed exceeds 0.3 times natural frequency, the SNR of vibration signal will be enhanced obviously in dynamic unbalance measurement. The calibration method proposed by authors can reduce the dynamic unbalance measurement error due to different rotor's mass and different rotating speed along with enhancing vibration signal when rotating speed is above 0.3 times natural frequency. The relation between unbalance mass and sensors’ signal is affected by several elements such as system damping, rotor's mass, rotating speed and so on. When rotating speed exceeds 0.3 times natural frequency, these elements cannot be all ignored. Meanwhile increasing rotating speed can bring advantage of enhanced vibration signals. And in this situation calibration result at one fixed rotating speed cannot reach permanent effective in a wide speed range. Thus an improved calibration method is presented here based on Cubic B-spline interpolation method. Cubic B-spline's characteristics fit the systems very well based on physical model and can help in getting more accurate interpolation results. Finally, experiments on CAB590 general balancing machine (SCHENCK, Germany) were set up and the improved permanent calibration method was proved effective and accurate enough.