High-quality-factor (Q-factor) mechanical resonators are indispensable components in quantum optomechanical experiments such as optomechanical cooling, quantum sensing, precision metrology and entanglement/squeezing generation. While the Q-factor measurement has been performed for high-frequency resonators with low Q-factor, the Q-factor measurement for a low-frequency resonator with high Q-factor is still challenging. It is difficult to identify the mechanical modes from the other noise source in the environment, such as audio noises of air fans and mechanical modes of clamps. Furthermore, the traditional piezoceramic transducer for driving the mechanical resonator has limited response speed. In this article, we employs the optical radiation pressure to directly drive the mechanical oscillator. The Q-factor is measured by the ring-down technique. With the help of precise controllable electrical current, the radiation pressure can be precisely controlled, thus providing faster response and broader operational bandwidth, especially in the acoustic and sub-acoustic frequency ranges. What’s more, this approach mitigates the low-frequency noise induced by environmental vibrations and experimental apparatus, which are difficult to isolate. In the experiment, we measure the Q-factors of a mechanical resonator array which includes tens of single mechanical resonators of different size and different structure. A single resonator consists of a single-crystal GaAs cantilever integrated with a micromirror. A laser beam, modulated by an acousto-optic modulator (AOM) acting as a fast optical switch, serves as the radiation pressure driving source. Another probe beam is reflected by the high-reflectivity micromirror of the resonator and detected by a quadrant photodetector (QPD) to obtain the ring-down signal from which the Q-factor is obtained. The results are compared with those obtained using traditional piezoceramic drive. The results show that in the low-frequency region (below ~2 kHz), where environmental noise coupling is pronounced, the optical drive method effectively suppresses low-frequency noises. The relative error of Q-factor measurements using optical drive is approximately 5%, lower than that obtained with piezoelectric drive. This optical radiation-pressure drive technique provides a robust and fast-response approach for measuring the Q-factors of massive low-frequency mechanical resonators.