Abstract: In order to realize the function of precise reverse phase and amplification of weak voltage signal,a new method of precise amplification of weak voltage signal is introduced in this paper. The inverse proportional addition circuit is used as the main circuit and the deviation between output signal and input signal is extracted by the electromagnetic unit and compensated into the main circuit to realize the dynamic adjustment of the output signal. The output signal is amplified to 5 V by means of series connection of several groups of separated windings. A precise two- stage isolated boost unit is designed to achieve electrical isolation between the secondary device and the secondary device. Meanwhile,the accuracy of the output voltage of the isolated transformer unit in the boost link and feedback link is ensured. The test results show that the output voltage ratio difference after boost with different proportion of separated winding is less than 10×10^{- 6},The angle difference is less than 20 μrad,so this method has a strong practical value in the field of voltage error calibration.