The utility model discloses a heat supply system for a factory boiler, comprising a boiler, a steam pipeline, a valve, a water supply tank for the boiler, a hot water pipeline and a steam trap, wherein the steam hole of the boiler is connected with gas-consuming equipment by the steam pipeline; the water supply tank for the boiler is used for supplying water for the boiler; and a condensed water outlet of the gas-consuming equipment is connected with the water inlet of the water supply tank for the boiler by the steam trap and the hot water pipeline. By adopting the steam trap, steam can be isolated so that condensed water can flow out, and the condensed water that flows out is circulated to the water supply tank for the boiler so as to be re-utilized by the boiler, therefore, the quantity of ion water of the boiler is saved; and water flowing out of the steam trap is hot, therefore, energy resources required to heat water in the boiler can be reduced.