We analyze states of polarization in the fiber with different pitches and the influence of the environmental temperature on the fiber from the high-birefringence pitch and the structure of the sensing fiber. We compare the temperature characteristics of PANDA fiber, elliptical core fiber, and polarization-maintaining (PM) microstructure fiber, and make the conclusion that for a given fiber optic current sensor (FOCS), when the pitch of the sensing fiber LT is twice as long as the beat length Lp of the fiber in non-helical state, the temperature characteristic is the worst; when LT decreases, polarization-maintaining ability and anti-physical-interference ability weaken; when LT≈Lp, the sensing fiber has good temperature characteristics and strong anti-physical-interference ability. The sensing fibers with different structures have different ratio errors. Without compensation at the temperature of -40-+70 ℃, the sensing fiber based on PM microstructure fiber has a minimum value of ratio error ±0.32%.