The thermal time constant is a key indicator of the uncooled infrared detector based on the microbolometer, it is highly related to the effective frame rate of the detector. Therefore, it is necessary to measure thermal time constant for device design and application. However, the typical design value or the measurement result based on mono-element is not easy to establish the quantitative relationship with the frequency-response characteristic of the detector. In this paper, a method for measuring thermal time constant based on array devices was introduced. The method employed a chopper to obtain a chopping frequency that was less than 1/2 frame rate, after the fast Fourier transform calculation, fitting the frequency response curve by the effective voltage response signals at different frequency point, the thermal time constant could be quickly and effectively extracted. By the experiment proving and results analyzing, the method has the advantages of high precision accuracy, strong anti-interference ability, good stability and short test time. What′s more, there is no special requirement for testing instruments or testing samples, and is worthy to be popularized.