The device of testing rotational speed is very important to dynamic-balancing testing system.Requirements for the device of testing rotational speed include: high-accuracy,stabilization,credibility,and shorter testing time.To the development of high-speed rotor dynamic-balancing testing system based on DSP(digital signal processing),the way of picking-up rotator reference signal,testing rotator speed based on DSP and the design of software are introduced.This new way of testing rotational speed in high-speed rotor dynamic-balancing testing system based on DSP is accurate,simple,convenient,the range of rotational speed which can test is broad,and the new way is very suitable to pick-up the amplitude and phase of vibration caused by unbalanced amount.