Abstract: In order to study hole protection by casing technology for large diameter extraction drilling, taking the first mining face at No.3 panel of Datong Coal Group Tashan Mine as the research background, the theoretical analysis, numerical simulation and field test are used to study the technology; according to the theory of plasticity, the analytical solution of the stress field in the plastic zone of borehole casing pipe and the ultimate strength of “casing-surrounding rock system” expression are deduced; FLAC^3D is used to analyze the stress distribution of large diameter borehole with or without hole protection by casing hole, and results are verified by field. With the advancing of working face, the influence range and strength of mining on large diameter borehole is gradually increased no matter with or without hole protection by casing; the ultimate strength with hole protection by casing is 3.47 times that of without hole protection by casing.