The invention discloses an ultra supercritical boiler with a parameter of more than 700 DEG C having a secondary re-heating function. A chamber of the boiler is horizontally placed, and a combustor is arranged on a front wall. A high temperature super-heater, a high temperature primary re-heater, a high temperature secondary re-heater, a low temperature super-heater, a low temperature secondary re-heater and a low temperature primary re-heater are sequentially arranged in a horizontal flue along the flow direction of the smoke; a coal economizer is arranged in two stages of a tail vertical flue; and a platen super-heater is arranged in the chamber of the boiler. Through the arrangement mode of the boiler disclosed by the invention, secondary re-heating of the unit can be realized; moreover, the temperature of the steam can be increased to more than 700 DEG C. The length of a high temperature steam pipeline is shortened to the maximum to reduce the construction cost while the efficiency of the unit is obviously improved. Through the invention, the efficiency of thermal power generating units in China is possibly improved to more than 50%.