A novel fiber used in extreme low temperature (-70℃) was designed, which includes the core layer, the inner cladding layer, the depression cladding and the outer cladding layer. The relationship between the bending loss and the refractive index difference was studied. By comparing the thickness and modulus of different coating layers, optimizing design of the fiber drawing process, a quartz fiber that can be used in -70℃ for a long time was manufactured. The experimental results show that the additional loss (-70℃) of the fiber at 1 550 nm and 1 625 nm is less than 0.01 dB/km, which provides reliable theoretical and experimental basis for the preparation and industrialization of extreme cold fiber and optical fiber composite overhead ground wire.