Based on a temperature sensing module of the fiber Bragg grating(FBG),temperature sensing characteristics of in FBG were studied,and the analytical formulae of temperature effective linear sensitivity coefficients was deduced.Responce characteristics of FBG in high temperature were analyzed.The way to reduce non-linear response in high temperature was proposed.The experimental result indicates that by improving thermal-expansion coefficients of encapsulation the non-linear response of FBG in high temperature can be reduced effectively.