In this paper, a kind of bidirectional electro-optic Mach-Zehnder intensity modulator was designed for microwave full-duplex transceiver system. According to the principle of modulation and superposition of electric signals to optical signals in the electro-optic modulator, analyzed is the deterioration of isolation caused by the distribution difference between the designed electric field and the actual electric field of the modulated electrode. By comparing the analysis, design and simulation results of different modulation electrode structures, it is concluded that the bidirectional electro-optic intensity modulator with the isolation better than -30dB above 3.5GHz is fabricated successfully, achieving an isolation better than -30dB in the range of 5~17GHz.