A high temperature fiber Bragg grating (FBG) sensing network based on wavelength modulation is highly developed on the basis of FBG high temperature sensing characters. A new packaged high temperature FBG sensor head is designed in this system. A high reliable distributed sensing network structure is also proposed to overcome the low reliability of the traditional FBG sensing network. Diffraction technique based on InGaAs image sensing is used to demodulate reflected wavelength. The results show that the average goodness-of-fit of sensing system′s temperature curve is 0.9991, the sensitivity is 0.0258 nm/℃, the accuracy is ±0.6 ℃ and the response time is less than 16 s. Moreover, the sensing network is steady enough for high temperature measurement.