Firstly， the phenomenon of signal noise frequency band overlapping and the effect of low frequency noise in the direct current optical transducer are analyzed. The direct current optical sensing spectrum shifting measurement method is presented，and the mathematical model of optical modulation and signal demodulation is developed. Secondly， the realization of direct current optical sensing spectrum shifting measurement method is designed. Finally， the error analysis and characteristic test are finished in the direct current optical transducer. The test results show that the proposed measurement system has high accuracy of direct current measurement， and can eliminate the signal noise frequency band overlapping phenomenon. The practicality of the proposed method is thus proven.