Abstract: The system of two-way telemetry for drilling can transmit drilling information from bottomhole to surface in real time, and send the order from surface to bottomhole at same time. Connecting with so called intelligent drilling tool like steering drilling device, the telemetry can monitor downhole drilling situation and also realize the remote control of downhole drilling tool at will. The electromagnetic type of two-way telemetry has developed in recent years owing to its advantages of being suitable to use for air/gas drilling or foam drilling. This paper introduced the history and development situation, the principle, structure and working parameters of self-made electromagnetic two-way telemetry. Experiments indicate that waveform has an effect on two-way electromagnetic transmission. Sine wave is better than square wave in resisting disturbance. There is higher error rate for square wave especially when received signals are very weak. In addition, the attenuation of downgoing signals is large compared with that of upgoing signals.