Due to the difficulties of judgments in magnesium and its alloys′ ignition points and problems of measured temperature field distribution influenced by thermocouples, short lifespan and inconvenient miniaturization, a new kind of colorimetric temperature test device is designed. The basic structure and test principle of this device are introduced. According to the inflection point of changes in two channels of received optical radiation, the burning time is confirmed and the corresponding temperature is just the ignition point. A fiber optic spectrometer is used to test the spectra before and after combustion, which provide a reference for choosing system′s wavelength and bandwidth, and temperature correction is performed with calculating the ratio of emissivity. A temperature of blackbody furnace is used to do static calibration for the colorimetric test device to decide the systematic wavelength and bandwidth. Finally, a CO2 laser is employed as the heat source to ignite pure magnesium and magnesium alloy AZ91D. The colorimetric temperature test device and infrared thermometer are used to do ignition test. The results test show that the relative error of pure magnesium and magnesium alloy AZ91D are 1.43% and 1.08%, respectively.