A 2 to 14 μm ambient infrared spectroradiometer based on linear variable filters with spectral resolution of 2% measurement wavelength is studied. According to the wavelength range limit of a single slice gradient filter, the coverage of the 2 to 14 μm wide band is realized by combining three pieces of variable filters with a spectrum fusion algorithm. By using a scheme containing a fine stepping motor and a position sensor to carry out fine spectrum splitting, the spectral resolution of 2% measurement wavelength is realized. By using the chopping and digital orthogonal lock-in amplifier scheme, the detection of weak infrared spectral signals is realized. For a stepping motor used to drive variable filters, the approximate function control algorithm and step frequency conversion acceleration motion law are used. Thus, fine step control and 0.1scan/second to 10 scan/second variable spectrum scanning speed are achieved. Finally, the calibration method and result of the spectroradiometer are presented.