The invention relates to a novel method for online monitoring flue gas heat load distribution of a spiral water wall of a supercritical boiler. A thermal coupler is spot-welded to the away-from-fire side of a key point of a characteristic pipe of the surface of the spiral water wall of the supercritical boiler, temperature signals are collected in real time through a conventional method and transmitted into a computer, and then the added enthalpy of working media between adjacent test points of the same pipe multiplied by the average working medium flow and divided by the radiation area equals to the average heat load between the two points. A heat absorption heat load distribution surface chart of the wall surface of the water wall in the direction of the height of a hearth can be obtained online according to the heat absorption heat load value, obtained in real time through smooth connection, of each pipe of the water wall, and the change situation of the heat absorption heat load of the water wall in the direction of the height of the hearth can be reflected in real time.