Abstract: Aiming at the problem of temperature monitoring of contacts and bus in BGP9L-6G high-voltage switches for underground substation,the paper proposed a design scheme of active temperature monitoring system based on optical fiber sensing technology.The system used AVR single-chip micro-(computer) to (control) optic source to emit optical signal and the optical signal entered optical fiber tempe-(rature) sensor through input optical fiber.Bimetallic strip in the optical fiber temperature sensor changed(deformation) caused by environmental temperature effect to upper and lower displacement,and optical(intensity) coupled into output fiber would change.After photoelectric conversion,the optical signal(modulated) and the (non-modulated) one by optical fiber temperature sensor entered LOG114 to be (logarithmic) and differential(amplified,) then LOG114 exported their current ratio.After A/D conversion and data analysis to the(current)(ratio,) the temperature value was obtained.The experiment result on high-low temperature test cabinet showed the system had high detecting sensitivity.