The main source of all fiber optical current transformer temperature error is caused by 1/4 waveplate temperature error and the sensing fiber Verdet constant temperature error. this paper analyzes the relationship of the total temperature error, the 1/4 waveplate temperature error and the sensing fiber Verdet constant temperature error, and derives the mathematical expression of them; the theoretical analysis results are verified by the test system of FOCT temperature error. the theoretical analysis results and test results show that when the 1/4 waveplate initial phase delay angle is , in the vast most of the temperature range the relative value of the error is less than 0.2%, it realizes compensation for temperature error.