High-quality-factor (Q-factor) mechanical resonators are indispensable components in quantum optomechanical experiments, including optomechanical cooling, quantum sensing, precision metrology, and the generation of entanglement and squeezing. Although Q-factor measurements have been performed on high-frequency resonators with low Q-factors, measuring the Q-factors of low-frequency resonators with high Q-factors is still challenging. It is difficult to identify the mechanical modes from other noise sources in the environment, such as audio noise of air fans and mechanical modes of clamps. Furthermore, the response speed of traditional piezoceramic transducer for driving the mechanical resonator is limited. In this study, we use the optical radiation pressure to directly drive the mechanical oscillator. The Q-factor is measured by the ring-down technique. With the aid of precisely controllable electrical current, radiation pressure can be precisely regulated, thereby providing faster response times and a broader operational bandwidth, especially in the acoustic and sub-acoustic frequency ranges. Furthermore, this approach reduces the low-frequency noise caused by environmental vibrations and experimental equipment, which are difficult to isolate. In the experiment, we measure the Q-factor of a mechanical resonator array composed of tens of individual mechanical resonators of different sizes and different structures. 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 a 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 a low-frequency region (below ~2 kHz), where environmental noise coupling is pronounced, the optical drive method effectively suppresses low-frequency noise. The relative error of Q-factor measurements using optical drive is approximately 5%, lower than that obtained with piezoelectric drive. This optical radiation-pressure driving technique provides a robust and fast-response method for measuring the Q-factors of massive low-frequency mechanical resonators.