  The design and optimization of the Electromagnetic Calorimeter (ECAL) are
crucial for the Circular Electron Positron Collider (CEPC) project, a proposed
future Higgs/Z factory. Following the reference design of the International
Large Detector (ILD), a set of silicon-tungsten sampling ECAL geometries are
implemented into the Geant4 simulation, whose performance is then scanned using
Arbor algorithm. At single particle level, the photon energy response at
different ECAL longitudinal structures is analyzed. At bi-particle sample, the
separation performance with different ECAL transverse cell sizes is
investigated and parametrized. The overall performance is characterized by a
set of physics benchmarks, including $\nu\nu H$ events where Higgs boson decays
into a pair of photons (EM objects) or gluons (jets) and $Z\to\tau^+\tau^-$
events. Based on these results, we proposed an optimized ECAL geometry for the
CEPC project.
