  A high-level beam background is a crucial challenge to future upgrades to the
BEPCII collider. We report on the first separate measurement of the main beam
background components at BEPCII. The separation measurement enables the beam
background extrapolation towards the beam parameters assumed for the upgraded
BEPCII. The measured rates of each background component are also compared with
a brand-new simulation based on SAD and Geant4. The discrepancy between
experiment and simulation remains 1$\sim$2 magnitudes after calibration with
beam lifetime, which should be further investigated.
