In order to solve the problem of internal space temperature field disturbance during observation process of LAMOST telescope

a space temperature monitoring method based on ultra-weak fiber Bragg grating（ UWFBG） is proposed. The temperature sensing principle of the single coating layer UWFBG sensors is theoretically analyzed. A kind of stress-free UWFBG temperature sensing cable is designed

and its temperature characteristics are calibrated. The temperature sensitivity is about 10. 8 pm/℃

and the linearity is prior to 0. 999 7 in the range of-20 ～ 50 ℃ . 23 armored UWFBG cables with a spacing of 1 m are laid along the M

B

mirror and the corridor of LAMOST to monitor internal te

mperature change in real time. Results show the evolution process of space temperature gradient in the MBmirror and the corridor

and influence of observation behavior and external environment on temperature distribution. It provides a reference for analyzing on temperature field inside large optical telescope.