The invention relates to a heat quantity apportionment measuring method and a device for central heating. In the method, aiming at a heating system of a switching-on/switching-off type heat supply control mode, the apportionment measurement of the heating heat consumption is carried out according to a switching-on/switching-off time area method, modification with the time is carried out on the opening time of a switching-on/switching-off valve according to an built-in special modification computation program by the real-time measurement of the water supply and return water temperature values of heating users, and accumulation is carried out to calculate a modified opening specific value; when the heating season is over, the final modified opening ratio and the heating area of each user are used for apportioning the total heat quantity to determine heating charge which needs to be charged by each user; and the special modification computation program is designed in such a way that under the opening state of the switching-on/switching-off control valve, the water supply temperature value and the return water temperature value are read, the modified opening ratio is calculated, so the apportionment of the heat quantity used by the users is calculated. The device is suitable for the heat quantity apportionment measuring method for central heating and comprises a room temperature controller, the switching-on/switching-off control valve, a water supply temperature sensor, a return water temperature sensor, a heat supply control/opening time modification integrating instrument and the special modification computation program.