The causes leading to problems discovered in control system during the process of debugging for digital electrohydraulic（DEH） governing system of the first home made 600 MW supercritical unit installed in Huaneng Qinbei Power Plant have been analysed. Through optimization improvement

the reset function of the emergency trip system（ETS） has been perfected

increasing the energy converted from power of decreasing automatically the speed up rate at the time in which the rotation speed of steam turbine to be nearing the normal rotation speed

eliminating large rotation speed fluctuation of the steam turbine during the time of small load rejection etc.. The results of practical operation and test show that the optimization improvement has obtained better effectiveness.