Abstract: Focusing in optics was extended to spectral dimension in this paper, and the method of spectrally focusing was proposed. The spectrally focusing was implemented by adaptively tuning of a F-P optical cavity tunable filter, which was controlled by the parameters from the regulation and control function driven by the differences between interesting object and its background. An hyperspectral imaging IR system with spectrally focusing was introduced, and the practical scheme of main subsystem was contrived, the mechanism and approach to spectrally focusing were investigated. With spectrally focusing, spectrally adaptive detection can be achieved, the hyperspectral images can be utilized more efficiently, and thereby the ability demand for image processing is reduced. Spectrally focusing conduces to make hyperspectral imaging IR system more rapid and compact, which suits with the utilization in missile or UAV.