  This paper presents theoretical integrated spectral energy distributions
(SEDs) of binary star composite stellar populations (bsCSPs) in early-type
galaxies, and how the bsCSP model can be used for spectral studies of galaxies.
All bsCSPs are built basing on three adjustable inputs (metallicity, ages of
old and young components). The effects of binary interactions and stellar
population mixture are taken into account. The results show some UV-upturn SEDs
naturally for bsCSPs. The SEDs of bsCSPs are affected obviously by all of three
stellar population parameters, and the effects of three parameters are
degenerate. This suggests that the effects of metallicity, and the ages of the
old (major in stellar mass) and young (minor) components of stellar populations
should be taken into account in SED studies of early-type galaxies. The
sensitivities of SEDs at different wavelengths to the inputs of a stellar
population model are also investigated. It is shown that UV SEDs are sensitive
to all of three stellar population parameters, rather than to only stellar age.
Special wavelength ranges according to some SED features that are relatively
sensitive to stellar metallicity, young-component age, and old-component age of
bsCSPs are found by this work. For example, the shapes of SEDs with wavelength
ranges of 5110-5250AA, 5250--5310AA, 5310--5350AA, 5830--5970AA, 20950--23550AA
are relatively sensitive to the stellar metallicity of bsCSPs. The shapes of
SEDs within 965-985AA, 1005--1055AA, 1205--1245AA are sensitive to
old-component age, while SED features within the wavelength ranges of
2185--2245AA, 2455--2505AA, 2505--2555AA, 2775--2825AA, 2825--2875AA to
young-component age.
