The invention relates to a wide-load heat supply energy-saving system of a back pressure type small turbine drive water supply pump. The wide-load heat supply energy-saving system comprises a main turbine, a back pressure type small turbine, a water supply pump, a boiler reheater, a deaerator and a low-pressure heater. The steam discharge end of a high-pressure cylinder in the main turbine is connected with the steam inlet end of the boiler reheater, the first steam outlet end of the boiler reheater is connected with the steam inlet end of an intermediate-pressure cylinder, and then a reheating circuit is formed. The second steam outlet end of the boiler reheater is connected with the steam inlet end of the back pressure type small turbine, and then a heat supply circuit is formed. The power output end of the back pressure type small turbine is connected with the drive input end of the water supply pump, and then the water supply pump drive circuit is formed. The first steam discharge opening of the intermediate-pressure cylinder is connected with the steam inlet end of the deaerator through a heat return and steam extraction pipeline, the second steam discharge opening of the intermediate-pressure cylinder is connected with the steam inlet end of a low-pressure heater through a steam extraction pipeline, and then a heat return circuit is formed. A steam extraction and supplementation structure of the heat supply circuit is formed between all connecting pipelines of the low-pressure heater, a condensate water pipeline, the deaerator and the intermediate-pressure cylinder and a heat supply pipeline network. The wide-load heat supply energy-saving system has the advantages that the heat supply running economy is improved, and the high running adjustment flexibility and heat supply economy are achieved.