  We study the photon detection efficiency and position resolution of the
electromagnetic calorimeter (EMC) of the BESIII experiment. The control sample
of the initial-state-radiation (ISR) process of $e^+e^-\rightarrow \gamma
\mu^+\mu^-$ is used at $J/\psi$ and $\psi(3770)$ resonances for the EMC
calibration and photon detection efficiency study. Photon detection efficiency
is defined as the predicted photon, obtained by performing a kinematic fit with
two muon tracks, matched with real photons in the EMC. The spatial resolution
of the EMC is defined as the separation in polar ($\theta$) and azimuthal
($\phi$) angles between charged track and associated cluster centroid on the
front face of the EMC crystals.
