Abstract: It is an effective means to drill directional long boreholes in coal seam for gas drainage. ZDY4000LD directional drilling rig can meet the demand of two kinds of drilling methods, i.e., down-hole motor drilling and rotary drilling. It is equipped with measurement while drilling system (MWD). It serves well as directional drilling equipment for most of coal mines in China. In this paper, simulations of chassis support system and main shaft braking system were introduced, some key technologies of hydraulic system, main shaft braking and gripper system were also represented. Author analyzed and concluded that directional drilling and MWD technology have been adopted by coal mine users, it has bright future in technology development, it is also important for gas drainage and deep coal mining.