A simulation program of BES trigger is described and a comparison of its re
sults with experimental data is presented. With this program, the efficienc
ies of BES trigger system for different kinds of events generated by Monte-
Carlo simulation are given for the first time and they are consistent with
those measured by the experimental method. It proves that this trigger simu
lation code is suitable for studying the performance of BES trigger system
and is a complement of BES Monte-Carlo simulation code library.