Abstract: In view of theory of elasticity and non-Newtonian fluid mechanics, this paper has studied the variables which are related to backtow loads. Methods for computing the three components of backtow resistance, mass of the pipe and the corresponded pipe-soil frictional force, drag induced by effect of bending resistance, slurry drag resistance are extensively analyzed. The backtow loads can be obtained based on the sum of the above three components and the static equilibrium condition. All of three kinds of resistance contribute very much to the backtow loads, besides; the weighted factors are also dynamically varied during the backtow process. The slurry drag resistance is an important part of backtow resistance. Including such a component can predict the dynamical characteristic of the backtow loads better. Based on the collected HDD installation & experimental data, the predication model is validated by practical examples. The coincident results between the predicted data and the experimental data show the correctness of the presented method.