  To measure the $R$ value in an energy scan experiment with $\ee$ collisions,
precise calculation of initial state radiation is required in event generators.
We present an event generator for this consideration, which incorporates
initial state radiation effects up to the second order accuracy, and the
radiative correction factor is calculated using the totally hadronic Born cross
section. The measured exclusive processes are generated according to their
cross sections, while the unknown processes are generated using the LUND Area
Law model, and its parameters are tuned with data collected at $\sqrt s=3.65$
GeV. The optimized values are validated with data in the range $\sqrt
s=2.2324\sim3.671$ GeV. These optimized parameters are universally valid for
event generation below the $D\bar D$ threshold.
