The invention discloses a reheat steam temperature control method of a four-corner tangential boiler under a low-nitrogen combustion mode. The method comprises the following steps: the advanced heat support is provided for variable load of a set through dynamic advanced feedforward in a main control loop of the boiler; a ratio of upper-layer powder feeders to lower-layer powder feeders is reasonably controlled; and an air volume ratio of a main combustion area to a burnout area is reasonably controlled. The method effectively solves the technical problems of easy movement of the flame center position of a hearth, difficulty of stable control of reheat steam temperature and in particular, increment of desuperheater water of a reheater due to the overheat phenomenon of the boiler caused by high fluctuation of the reheat steam temperature under the working condition of variable load.