The invention discloses a device and method for measuring the surface temperature of an object through the relative strength of reflected light, relating to an object surface temperature testing method. The device is provided with current sources, an infrared LED light source, lenses, a wave chopper, a spectrograph, a photomultiplier, a phase-locked amplifier, a voltmeter, a computer, a temperature controller and an optical fiber, wherein an objected to be measured is respectively connected with the temperature controller and the second current source; the infrared LED light source is connected with the first current source; the first lens is arranged between the infrared LED light source and the wave chopper; the second lens is arranged above the wave chopper; rays emitted by the infrared LED light source are converged by the first lens, and direct-current rays are changed into alternating-current rays through the wave chopper; the reference signal output end of the wave chopper is connected with the phase-locked amplifier; light collected by the second lens is irradiated on the surface of the objected to be measured; the reflected light is additionally collected and converged through the third lens; the light converged by the third lens is collected by the spectrograph; the spectrograph is connected with the photomultiplier; the photomultiplier is connected with the phase-locked amplifier; the phase-locked amplifier is connected with the voltmeter; and the voltmeter is connected with an input port of the computer.