The paper mainly introduces CYG-300 type multifunctional full hydraulic drilling machine about its overall structure design and hydraulic system design as well as main function. The load feedback system is adopted with dynamic head double hydraulic motors and two-gear manual transmission to output 4 different stepless torques and rotating speeds; related control valve is set for feeding circuit in hydraulic system to increase rotary spray function of the machine, all of these make the rig suitable for wider range with more functions. The field test drilling shows that this hydraulic system has good operation condition, strong drilling ability and convenient operation.