  The discovery of an excess of light in the far-ultraviolet (UV) in 1969 in
elliptical galaxies was a major surprise. While it is now clear that this UV
excess (UV-upturn) is probably caused by an old population of helium-burning
stars. Han et al (2002, 2003) proposed a binary model for the formation of hot
subdwarfs (helium burning stars) and the model can reproduce the observations
in our Galaxy. By applying the binary model to the study of evolutionary
population synthesis, we have obtained an {\it a priori} model for the
UV-upturn of elliptical galaxies. The model shows that the UV-upturn is most
likely resulted from binary interactions and it is universal (not very much
metallicity-dependant) in ellipticals. This has major implications for
understanding the evolution of the UV-upturn and elliptical galaxies in
general; contrary to previous postulates, it implies that the UV-upturn is not
a sign of age, but could be a potentially powerful indicator for a recent minor
burst of star-forming activity.
