Abstract: When horizontal directional drilling is used to cross large river, undesirable formations like loose and soft ones will frequently be encountered at the soil in and out ends. For purpose of successful drilling, the methods like geologic reclamation or casing isolation are usually used to improve the hole making performance. In this paper, considering the existing casing ramming installation technologies, through analyzing the mechanical force status in casing ramming process, a casing ramming process stress model is established with the analog simulation technique to conduct numerical simulation on casing stress status and reveal the effect of different factors in casing ramming process on the rammed depth. The numerical simulation analysis results show that the resistance to buckling can be effectively increased by enhancing the material strength of casing. As the rammed depth increases, the transmission efficiency of ramming force drops rapidly. In addition, with relevant mechanical theories, referring to push pipe architecture computation method, and combining theoretical analysis with field operation status, a computation method of casing limit rammed depth is proposed, which can provide reference for the design of effective casing rammed depth.