Slag slipping wells are often used in the projects of mining and tunneling, which can be dredged through drilling with casing by using top head drilling machine and wire-line core drilling tools to deal with the frequent clogging accidents. Based on the example of the slag slipping well dredging construction in Xiaolangdi Dam Yellow River diversion project, this paper introduces the dredging methods, supporting equipments, operation rules and attentions, summarizes the experience and deficiency of the drilling with casing to provide practical reference for similar dredging projects.