GYD-300 fully hydraulic driving head engineering rig is a model of fully hydraulic driving and driving head reverse circulation. Hydraulic system is operated by electro-hydraulic with integrated structure of cartridge valve. PC monitoring system was used to monitor pressure at the bottom of borehole; according to the monitoring data of different formations to set different drilling pressure, so automatic and manual constant pressure drilling were realized. The paper introduced the rig on its structural feature, experiment and main technical parameters.