To overcome the effect of polarization-maintaining fiber delay polarization crosstalk on the measuring accuracy of an all Fiber Optical Current Sensor (FOCS), the polarization error of the FOCS was studied by using the Jones matrix. The error model for the polarization-maintaining fiber delay polarization crosstalk was simplified, and the relation between the polarization crosstalk and the output was deduced based on the simplified model. The influences of the polarization crosstalk on FOCSs normalized scale ratio under a normal temperature and variable temperatures were analyzed respectively by simulation and analysis. The comparison between the experiment results and theory conclusions show that the simplified model is reasonable and the simulation result is correct. The actual temperature characteristic of the polarization-maintaining fiber delay polarization crosstalk was tested. Experimental results indicate that when there is polarization crosstalk in the fiber delay line, the ratio error of the FOCS is proportional to the current;when the current is constant, the higher the polarization crosstalk is, the higher the FOCSs ratio error is. Finally, the fluctuation range of the fiber delay line polarization crosstalk to meet the 0.2S class error of FOCS was put forward.