On the basis of requirements of the closed-loop driving system in a liquid suspended rotor gyroscope for measurement of rotor speeds, a Back-electromotive Force (EMF) rotating speed detection method is proposed for the suspended rotor gyroscope. As induction coils work on Lenz's law, the rotating speed of rotor can be measured by detecting the back-EMF generated by a permanent magnetism (p-m) rotor. Because the detecting coil and driving coil share the same stator core, this method reduces the complexity of the stator, but also introduces a burr interference from the driving rectangular wave. The interference signal is then attenuated by an analog low-pass filter and sampled by an A/D converter. Finally, the rotating speed of rotor can be calculated automatically by using a Micro-controller Unit (MCU) and the zero crossing detection algorithm. The test results show that the relative error of detected value can be within 0.3%, and the nonlinear error is 0.41% when a refresh frequency is 4 Hz and the rotating speed reaches 5 000 r/min. The performance meets the requirement of rotating speed detection.