The invention relates to a steam turbine generator unit comprehensive waste heat utilization system and method. The system comprises a main steam power generator unit, a back pressure type small steam turbine generator unit, a heat supply network peak heater, a heat pump unit and a cooling tower system. A steam outlet of a high and intermediate pressure cylinder communicates with a steam inlet of a low pressure cylinder through a first steam conveying pipeline, the steam outlet of the high and intermediate pressure cylinder communicates with a steam inlet of a back pressure type small steam turbine through a second steam conveying pipeline, the steam outlet of the high and intermediate pressure cylinder communicates with a steam inlet of the heat supply network peak heater through a third steam conveying pipeline, and the steam outlet of the high and intermediate pressure cylinder communicates with a steam inlet of the heat pump unit through a fourth steam conveying pipeline. Heat supply network return water is input into the heat pump unit to be heated for the first time, heat supply network water supply enters the heat supply network peak heater through a hot water conveying pipeline which communicates the heat pump unit with the heat supply network peak heater to be heated for the second time, and finally heat supply network water supply is output through the heat supply network peak heater.