In order to meet the requirements of safe operation and external wall temperature monitoring of gasifier, based on the principle of Raman scattering effect and the characteristics of distributed optical fiber system, a novel temperature measurement method for on-line monitoring of gasifier external wall temperature is proposed, A kind of armored polyamide high temperature resistant distributed optical fiber sensor system using seamless steel tube as protective layer is designed. The temperature uncertainty experiment and data analysis of the sensor system are carried out. Finally, the temperature of the high temperature resistant optical fiber is tested on the experimental platform of gasifier outer wall temperature rise. The experimental results show that the temperature measurement range of the distributed optical fiber sensing system is 0~300 ℃, and the temperature measurement accuracy is ±2 ℃, the abnormal high temperature can be distinguished.