The invention relates to a distributed optical fiber Raman temperature monitor for a granary based on the pulse coding technology for granary safety detection, and belongs to the field of grain reserve. The temperature monitor is characterized in that the temperature monitor comprises a temperature measurement optical cable in the granary; a temperature measurement demodulating module which consists of a laser light source, an acousto-optic pulse modulator, an optical fiber bidirectional coupler, an optical wavelength division multiplexer, an avalanche diode, an amplifier, a signal processor and a PC host; a communication module, an alarm module and a remote client for monitoring. When the laser light source injects optical pulses into the optical fiber, a part of Raman scattering light closely related to the temperature can be generated and positioned through the optical time domain reflection technology, the signal-to-noise ratio is improved through the simplex cyclic encoding and decoding technology, and the temperature of a point to be measured can be obtained. The invention provides a safe, practical and high-sensitivity granary temperature measurement monitor, aiming at solving the problems of time and labor waste, low accuracy, electronic monitoring short circuit, limited sensing points, easiness in causing a fire and the like of manual inspection in the granary at present.