The invention discloses a device for measuring the heat effect in an isothermal hot reaction process of carbonaceous macromolecules. The device comprises three parts, namely, a thermal reaction system, a measuring system and a control system, wherein the thermal reaction system comprises a reaction kettle cover, a reaction kettle, a thermal insulation layer, an electromagnetic heating furnace body, a sample loading device, a vacuum system and a gas supply system; the measuring system comprises a sample thermocouple, a reference thermocouple, a cold-junction thermocouple and a temperature data acquisition system; the control system comprises a reaction device program temperature controller. The invention further provides a method for measuring the heat effect in the isothermal hot reaction process of the carbonaceous macromolecules by the aid of the device. The relation between the integral area of a temperature difference curve of the heating melting process of a standard substance and the melting heat effect is measured, and the integral area of a temperature difference curve obtained through actual measurement of the carbonaceous macromolecules is converted into the corresponding heat absorbing and releasing effects.