Initial State Radiative Correction in R Measurement at BES

Three typical schemes of the initial state radiative correction in e +e - collision through single photon annihilation were reviewed, and the numerical results were calculated in the energy region of 2—5GeV. The differences of the theoretical values of radiative correction factors (1+δ) are about 1%—2%. The uncertainty of the effective (1+δ obs ) is estimated to be about 2%—3%.