In order to improve the sensitivity and accuracy and reduce the noise of DC current comparator, the key link demodulation method was researched. Describe the working principle of two demodulation methods of DC current comparator; design the corresponding circuit and build the simulation model. The result shows that both methods can realize the function of converting the output signal of detection winding to the corresponding DC voltage. The important advantage of peak difference demodulation is that it can demodulate all even harmonic signals. A high detection gain will be obtained accordingly, which is favorable to increase sensitivity and accuracy. But the ripple of secondary current is large. Narrow band characteristics of phase sensitive demodulation are beneficial for reducing the system noise level; the ripple of secondary current is very small. As only second harmonics are demodulated, it is necessary to satisfy the best condition to achieve high sensitivity.