The invention relates to a dual-pressure DQC residual heat boiler that comprises a flue gas system, a high-pressure boiler barrel, a high-pressure evaporator, a high-pressure economizer, a superheater and a water-cooling wall and etc. A flue gas channel in the flue gas system is composed of a low-pressure self-deoxidizer system at the outlet of the high-pressure economizer; the low-pressure self-deoxidizer system is provided with a low-pressure evaporator; the inlet and outlet to the low-pressure evaporator are respectively connected with the low-pressure boiler barrel through a low-pressure evaporator descending pipe and a low-pressure evaporator flow riser; the lower part of the low-pressure evaporator is composed of the low-pressure economizer; the inlet to the low-pressure economizer is linked to the boiler water supply pipe; the outlet is connected with the low-pressure boiler barrel through the outlet pipe; the low-pressure boiler barrel is mounted with a deoxidizer head and a high-pressure delivery pipe; the area between the inlet and outlet to the low-pressure economizer is composed of a bypass pipeline; the bypass pipeline is provided with a circulating pump and a governor valve; the area between the low-pressure evaporator and the low-pressure evaporator descending pipe is composed of a low-pressure evaporator inlet collection tank; the area between the low-pressure evaporator and the low-pressure evaporator flow riser is composed of a low-pressure evaporator outlet collection tank. The invention effectively resolves the problems in prior arts of low heating efficiency and too much land resources.