-Sagnac fiber optic current sensor(S-FOCS) is a kind of precision instrument based on optical polarization and optical interference theory. There are several kinds of error characteristics from optical components in S-FOCS, including polarizer, integrated optical chip, quarter-wave retarder, sensing head and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. Focused on optical polarization error in S-FOCS, we analyze the characteristics of polarization errors associated with optical components in S-FOCS theoretically, and we demonstrate the methods to build optical polarization error models by using Poincare sphere and Jones matrix respectively. Then, based on model of polarization state in S-FOCS, we carry out simulation of polarization error characteristics in S-FOCS, and theoretically investigate the influence of several main error factors on optical polarization characteristics, including polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and PM fiber.