This study focuses on the operation process of steam turbine generator by using the Preliminary Hazard Analysis to identify the possible hazards. The results of this study show that there are seven risk factors in the operation process. However, the most serious risk factors are the broken slop drain pipe and furnace pipeline. These risk factors will cause the generator shut down. Thus, three solutions are proposed as follows: (1) Install the fixed U-bolts; (2) Add chemicals to the cooling water; (3) Install the deaerator. After evaluating these alternatives, installing the fixed U-bolts is the most effective way. Besides, adding chemicals to the cooling water and installing the deaerator simultaneously can significantly reduce the possible accidents in the process of operating steam turbine generator.