The operation of power generation cycles and their related events are one of the main issues in the field of safety of power plants. If these events are not properly managed for any reason, the consequences will be irreparable. In the meantime, the operator action can be one of the most effective factors in the management of the accident. In this research, the operator action has been evaluated in the main steam line break connected to the turbine and total loss of steam generator feed water for the Bushehr power plant. Firstly, the data has been validated in both steady and transient states with the final safety analysis report of the power plant of Bushehr as a reliable reference. The results indicate a good agreement with the final safety analysis report. In the next step, the operator action has been evaluated to mitigate the thermohydraulic parameters, including temperature and pressure. Finally, by performing an operator sensitivity analysis in the main steam line break connected to the turbine followed by total loss of steam generator feed water, the maximum possible time for operator intervention has been estimated 76 minutes.