The invention discloses an optical fiber radiation thermometer based on a colorimetric method, and belongs to the field of high temperature measurement. The thermometer comprises an optical system and a circuit system, wherein lenses of a lens group are connected with a high-power Y-type power transmission optical fiber to form the optical system; the circuit system adopts signal dual-channel processing and comprises photoelectric detectors, a preprocessing module, a preamplifier, an AD sampling module, a signal processing module, a display module, a keyboard input module and an information interaction module. Signals are divided into two paths via the power transmission optical fiber and transmitted to the corresponding photoelectric detectors, optical signals are converted into current signals, the current signals are converted into voltage signals via the preprocessing module and the pre-amplification module, the signal processing module adopts a curve fitting algorithm for analysis, sampling signals are obtained, a corresponding temperature value is calculated through calibration, and difference setting is further improved through the interaction module. The optical fiber radiation thermometer structure based on the colorimetric method can be applied to measurement of a crystal furnace thermal field.