In this paper,a new type of reflex electro-optic modulator is propose d.To illustrate the performance of reflex electro-optic modulator in synchronous homodyne coherent system,the eff ect of a 40Gbit/s dual polarization quadrature phase shift keying (QPSK) system is emulated with the Op tiSystem14.0software.The exper imental results show that the signal can be received well and the modulation and demodulation of the signal ca n be completed.The system works out the problem of the optical phase lock loop . The performance of the reflex electro-optic modulator in the system is superior.It may be used to achieve sy nchronous homodyne coherent reception system.It will play a guiding role in prac tical engineering.