Fluorescence resonance energy transfer (FRET) is an important photophysical mechanism which finds many applications in biophotonics, particularly in biological sensing and imaging. It is well known, there are two major factors that determine the efficiency of FRET. One is the distance between the donor and the acceptor, and the other is the overlap of the donor's emission and the acceptor's absorption spectra. However, while the distance-modulation of FRET is very popular, the spectral-overlap-modulation draws much less attention. In this talk, I would like to illustrate the importance of the strategy of spectral-overlapmodulation. The presentation will include our works on the construction of highly efficient FRET systems featuring the short and rigid linker between the donor and acceptor moieties, and several typical examples of spectral-overlap-modulation strategy applied in the development of ratiometric sensors.