The utility model discloses a process unit heating a simple-distillation tower by utilizing secondary steam generated by circular heating of clear liquid, which comprises a mash tower reboiler (1), a gas-liquid separator (2) and a clear liquid pump set (3), wherein the input port of the gas-liquid separator (2) is set to be communicated with a clear liquid input port from a distiller grain separation working section; the liquid output port of the gas-liquid separator (2) is set to be communicated with the device of an evaporation working section by the clear liquid pump set (3); the gas output port of the gas-liquid separator (2) is set to be communicated with the input end of the inner circulation of the mash tower reboiler (1); the output port of the inner circulation of the mash tower reboiler (1) is set to be communicated with the input port of a simple distillation tower (4); the input port of the outer circulation of the mash tower reboiler (1) is set to be communicated with an alcohol steam port of a rectifying tower; and the output port of the outer circulation of the mash tower reboiler (1) is set to be communicated with the input port of a return tank so as to lower energy consumption and reduce abrasion on the device.