The steam generator level control is the most difficult control system in nuclear power plant. It is a typical non-linear and lagging control system. It is affected by many factors, such as feed-water flowrate, steam flowrate, feed-water temperature and average temperature of primary system. Over the years, the reactor trip events caused by improper control of steam generator level in nuclear power plants are common. Based on the steam generator level control system of the GEN-II nuclear power plant, optimizations are carried out in a GEN-III nuclear power plant. The narrow range feed-water flowrate sensors are added to optimize the steam generator level control at low power. The optimized feed-water flowrate controller reduces the coupling with the feed-water pump speed control system. The valve characteristic curves are added to improve the control accuracy. The feed-forward control based on the pressure difference of the valve is added to optimize the steam generator level control during the conditions of losing one main feed-water pump. Finally, the performance of the steam generator level control system is largely improved.