The low-voltage output analog signals of direct circuit voltage transformers （DCVTs） are transmitted through cables without electrical isolation and are susceptible to electromagnetic interference. A scheme for transmitting analog signals with high linearity using optical fibers is designed. Using dual light sources and photodetectors to form a transmission channel and a closed-loop negative feedback channel, the photodetector in the negative feedback channel converts the current and feeds it back to the input end to suppress the nonlinearity of the electro-optical transmission coefficient. The nonlinear suppression control strategy and effect are analyzed through a control system model, and the key elements of the circuit design of the analog signal fiber optic transmission system are analyzed. A comparative test is conducted on the nonlinear characteristics of open-loop transmission and closed-loop feedback transmission of analog signal fiber optic transmission systems. The results show that the nonlinear error of analog signal fiber optic transmission is reduced from a few percent to within ± 0.05 % through the closed-loop negative feedback transmission scheme. Finally, the analog signal fiber optic transmission system is applied to DCVT for linearity testing. The experimental results show that the analog signal fiber optic transmission system can be well applied to the application requirements of electrical isolation and elimination of electromagnetic interference of analog signals in DC distribution networks.