Hydrological observation hole used to be bored on the ground in Zhengzhou coal mine area. Because of the high costs of construction and maintenance, underground hydrological observation hole is popularized gradually in recent years. High pressure water exploration and drainage was listed in the research subject of key technology of flood prevention and equipment by SACSS in 2013. As downhole drilling technology and equipment are becoming more and more mature, especially some technological difficulties are overcome one after another, such as special underground water48 exploration and drainage drill, orifice blowout prevention device, drilling with casing technology in soft and fractured formation and effective directional drilling technology in hard rocks, intrinsically safe operation has been realized for underground drilling in coal mine. In view of the particularity of underground coal mine drilling, the paper mainly expounds the difficulties and solutions in the construction of hydrological observation holes, including equipment selection, hole positioning, DTH drilling with casing in fractured formation; cementing and well control & blowout prevention, as well as acidification well washing after completion and so on.