A fault diagnosing method based on a simulated vaccine is provided. The fault diagnosing method comprises steps of: establishing a dynamic simulation model for simulating a start-up operation and a steady-state operation of a technological process according to process information, an operating procedure and historical data of the technological process; running the dynamic simulation model; extracting data within a first predetermined time from the simulated normal sample set to generate a normal simulated vaccine, and extracting data within a second predetermined time from the simulated fault sample set to generate a fault simulated vaccine; acquiring the historical data of the technological process; obtaining an immune antibody coefficient of the normal simulated vaccine, and generating a normal antibody library; and obtaining an immune antibody coefficient of the fault simulated vaccine, and generating a fault antibody library according to the fault simulated vaccine.