The invention discloses a thermal power generating unit FCB (Fast Cut Back) function evaluation method. A turbo generator set includes a thermal power generating unit which takes coal, oil and combustion gas as fuels to generate steam to drive a steam turbine to work. Aiming at that the FCB function thermal power generating unit is used as a black-start power supply and participates the black-start process, the FCB function evaluation method can realize evaluation of the FCB function size for the thermal power generating unit, evaluation of the FCB function capability for the thermal power generating unit, and evaluation of the capability that whether the thermal power generating unit can realize the FCB function through technical transformation. The FCB function evaluation method can evaluate the situation for realizing the FCB function for the thermal power generating unit in a regional power grid, and can provide a technical basis for the regional power grid to select the thermal power generating unit as the black-start power supply and to make a black-start plan.