A magnetic suspension thermobalance based on quick photothermal heating comprises a sealed container, a reaction tank, a magnetic suspension device, a laser displacement monitoring component, a photothermal heating component and a photothermal heating component displacement device. A method comprises following steps: weighing a testing sample and adding same into the reaction tank; putting the reaction tank into the sealed container together with a magnetic suspension float; causing the magnetic suspension float to float in the sealed container; introducing gas into the sealed container; measuring the real-time position of the magnetic suspension float, and causing same to a measurement zero point; heating the reaction tank; maintaining a heating beam on the reaction tank; measuring the temperature of the testing sample in the reaction tank; and recording the displacement of the magnetic suspension float, and converting said displacement into mass.