A system for transmitting optical differential signal includes: an optical source configured to generate two channels of optical signals having different wavelengths; an input end for a to-be-modulated electrical signal configured to input a to-be-modulated electrical signal; a unique optical modulator configured to perform optical modulation on the two channels of optical signals using the to-be-modulated electrical signal, to obtain two channels of modulated optical differential signals; an optical sending unit, configured to send the two channels of modulated optical differential signals to optical transmission media; an optical receiving unit, configured to receive the two channels of optical differential signals; an optical detector, configured to perform optical-to-electrical conversion separately on the two channels of modulated optical differential signals, to obtain two channels of electrical signals; and a comparator configured to perform a differential operation to obtain one channel of electrical signal.