The invention provides a distributed high precision temperature monitoring system and method in high-altitude permafrost regions, and relates to an observation device and a measurement method in civil engineering monitoring field. The objectives are to solve the problem of limited measurement range in the current temperature measurement method for permafrost regions, and satisfy requirements of working stability and durance of a sensing system in an extreme environment imposed by roadbed temperature measurement of high-altitude permafrost regions. According to the invention, a distributed temperature sensing fiber penetrates a temperature measurement steel pipe and is embedded under a roadbed surface layer; the temperature measurement steel pipe is filled with in-site soil of a to-be-measured roadbed; a quasi-distributed fiber bragg grating temperature sensor is fixed on the outer wall of the temperature measurement steel pipe; a fiber bragg grating demodulator is used for acquiring temperature distribution of the fiber bragg grating temperature sensor; and a Brillouin distributed temperature demodulator is used for acquiring temperature distribution of the distributed fiber bragg grating temperature sensor and calculating the temperature distribution according to the acquired data. The system and the method are suitable for roadbed temperature measurement in high-altitude permafrost regions.