Aiming at providing a mark post for protecting an underground pipeline, which can indicate, on the ground, the exact position of the pipeline buried underground so as to omit the construction of unnecessary pipelines to improve economic efficiency, the utility model provides a mark post to protect an underground pipeline and to indicate the position of the pipeline. The mark post is cylindrical and can be buried under the ground vertically with the top exposed outside; a horizontal through hole is arranged at the bottom of the mark post and the pipeline threads through the through hole. The mark post has the good effects that the position of the underground pipeline is indicated with precision and the mark post is guarded against being pulled out by external force.