The invention discloses a method and system for checking a power-supply coal consumption rate of a cogeneration unit during a heat supply period. The method comprises the following steps: step one, determining the boiler efficiency and heat rate of a cogeneration unit in a condensing state during a non-heat supply period step two, after ending of a heat supply period, carrying out statistics of heat supply parameters of the set during the heat supply period, and calculating a main steam enthalpy, a reheating steam enthalpy, a cold-to-heat steam enthalpy, a heating steam extraction enthalpy, a water supply enthalpy, and a heating water returning enthalpy respectively by inquiring water and steam property tables; step three, according to a designed heat balance diagram of the heat supply period of the cogeneration unit, calculating a boiler inflow coefficient and a reheating steam share of a heating steam extraction flow; step four, introducing parameters in the step twp and the step three into preset calculation formulas for calculating a power sent out by the heating steam extraction flow and a power sent by a condensing steam flow to obtain a corresponding power sent out by the heating steam extraction flow and a corresponding power sent by the condensing steam flow; and step five, calculating a heat rate and a coal consumption rate of the set during the heat supply period.