The invention discloses a day-ahead plan safety checking method based on research states. The method comprises steps of according to research requirements, selecting power grid day-ahead operation real-time mode data or stored history mode data to serve as the basic power grid operation mode for the day-ahead plan safety checking; loading the selected basic mode into an application owned by a user and displaying basic state tide information on a factory station map; carrying out operation mode adjustment, and modifying investment and stopping states or measurement values of a circuit breaker, a disconnecting link, a bus, a circuit, a transformer and a generator; and carrying out basic state safety analysis on the basic state tide mode with the adjusted mode, and estimating device overload, cross section threshold crossing and bus voltage thread crossing conditions. In this way, tide and voltage thread crossing conditions are adjusted and eliminated further, so the basic tide cross section required by the research is obtained. A practical and effective method is provided for adjustment and safety checking of the day-ahead plan mode of the electric power system.