  In this paper, we systematically studied blue stragglers produced from
primordial binary evolution via a binary population synthesis approach, and
examined their contribution to the integrated spectral energy distributions of
the host clusters. The mass transfer efficiency, $\beta$, is an important
parameter for the final products (then blue stragglers) after mass transfer,
and it is set to be 0.5 except for case A binary evolution. The study shows
that primordial binary evolution may produce blue stragglers at any given times
and that different evolutionary channels are corresponding for blue stragglers
in different visual magnitude regions (in V band) on the colour-magnitude
diagram (CMD) of clusters. The specific frequency of blue stragglers obtained
from primordial binary evolution decreases with time first, and then increases
again when the age is larger than 10Gyr, while that from angular momentum loss
induced by magnetic braking in low-mass binaries increases with time and
exceeds that of primordial binary evolution in a population older than 3 Gyr.
Meanwhile, blue stragglers resulting from primordial binary evolution are
dominant contributors to the ISEDs in ultraviolet and blue bands in a
population between 0.3 and 2.0 Gyr. The value of $\beta$ significantly affects
on the final results. For old open clusters, the assumption of $\beta =1$ when
the primary is in HG at the onset of mass transfer matches the observations
better than that of $\beta =0.5$ from the locations of BSs on the CMDs. Our
study also shows that, for most Galactic open clusters, the specific frequency
of blue stragglers obtained from our simulations is lower than that of
observations, which is puzzling.
