The invention relates to the technical field of optical tests, in particular to an external field type infrared radiometer. According to the infrared radiometer, a main convergence mirror is connected with a wave chopper; the wave chopper is connected with a standard reference black body source and light filters; the light filters are connected with neutral attenuation pieces; the neutral attenuation pieces are connected with optical spectrum correcting pieces; the optical spectrum correcting pieces are connected with an infrared detector; a signal acquisition part is connected with the infrared detector and the wave chopper respectively. Through the embodiment, a corresponding optical spectrum curve of a whole system in a measurement waveband can be enabled to be a flat curve through the optical spectrum correcting piece, the linearity and the measurement accuracy of the whole system are improved, and the influence of a radiation spectrum of a tested object on a measurement structure is avoided; the neutral light filters with different attenuation ratios are adopted and the dynamic range of equipment is expanded. Therefore, the equipment has a plurality of ranges and strong and weak radiation targets can be measured.