A system for testing thermal response time of an uncooled infrared focal plane detector array and a method therefor is provided. The system comprises: a blackbody, a chopper, a detector unit under test and a testing system. The method comprises: emitting radiation by the blackbody, chopping by the chopper, then radiating the radiation to the uncooled infrared focal plane detector array under test; generating different responses on the radiation at different chopping frequencies by the uncooled infrared focal plane detector array under test; collecting different response values of the uncooled infrared focal plane detector array under test at different chopping frequencies; obtaining response amplitude at a corresponding frequency in a frequency domain by FFT; fitting according to a formula Rv ⁡ ( f ) = Rv ⁡ ( 0 ) 1 + ( 2 ⁢ π ⁢ ⁢ f ⁢ ⁢ τ ) 2 to obtain the thermal response time.