The invention relates to an uncooled far infrared thermal imaging system, belonging to the technical field of infrared thermal imaging. The uncooled far infrared thermal imaging system comprises a chopper, a far infrared light lens, a light splitter, an infrared focal plane array, a near infrared light source, a near infrared light lens, a near infrared light filter, another near infrared light lens and a digital camera; and the core component is the infrared focal plane array, the array structure of the infrared focal plane array is a thin film filter in an F-P cavity structure and the material of the cavity is alpha polycrystalline silicon, and the two sides of the cavity are provided with multiple film layers which are alternately formed by alpha polycrystalline silicon thin films and Si3N4 thin films to form a mirror surface structure. In the invention, on the basis of thermo-optic effect principle of the F-P cavity thin film filter, a measuring method of integrated optics is adopted and converting, demodulating and imaging on the optical wave are carried out, so that an interior reading circuit is eliminated and Johnson noise is avoided; meanwhile, vanadium oxide or pyroelectricity material which is usually not matched with silicon can be avoided from being used, devices are highly integrated without influence on the performance thereof, volume is reduced, producing stepsand vacuum packaging cost are reduced, and cost can be greatly reduced; therefore, the uncooled far infrared thermal imaging system provided by the invention has certain application potential.