Quality factor is a key parameter determining the performance of the micro-machined gyroscope. The conventional measurement, the half-power bandwidth method, is low in efficiency, since it requires the user to store and deal with a multitude of amplitude-frequency response data. Based on the analyses on the dynamics model, the quality factor can be calculated according to the resonance frequency and first derivation of the phase-frequency function at the resonance frequency point, and the phase-frequency graph is approximately linear near the resonance point. Upon these characteristics, an online and quick quality factor measurement method was put forward. First, the gyroscope was excited near the resonance point to obtain the phase-frequency data. Then, the slope of the phase frequency was estimated by using the recursive least squares method. Finally, the quality factor was obtained according to the slope and the resonant frequency. The simulation and experimental results verify the correctness and feasibility of the proposed method.