In horizontal directional drilling, reamer drilling in soft and hard sandwiching often suffers from excessive wear, broken cutting teeth, swapped cones, and catastrophic buried well accidents. In order to study the reamer′s vibration influence on soft and hard sandwiching, a nonlinear dynamics finite element model was established that was composed of a cone reamer entity and a three-dimensional rock. The results showed that the peak and root mean square of the reamer′s lateral acceleration were respectively 5.3 and 5.2 times higher than that under the axial vibration in the soft and hard sandwiching, thus indicating that reamer premature failure was owed to severe lateral vibration. Meanwhile, the centralizer for the reamer drilling in the soft and hard sandwiching significantly reduced the lateral vibration intensity by 77.6% and increased the penetration rate by 57.5%. Optimal parameters of the centralizer were determined for the damping effect in the soft and hard sandwiching based on the Baker Hughes BHA vibration grading standards.