Study of BESII backgrounds

The BES II backgrounds experiment and simulation are described. In the experiment, we have studied the characteristics of the beam-related backgrounds.. In the simulation, we simulate carefully the beam-gas backgrounds with the mature tools-TURTLE and Geant3. Finally, we compare the, results of the experiment and those of the simulation, they agree with each other within a factor of 4, which is acceptable in background simulation. This comparison proves the simulation tools are reliable, which makes it possible for us to simulate the beam-related backgrounds of the future BES-BES III.