The ancient Badu landslide was reactivated due to heavy rainfall and excavation, and thus drainage in the landslide could be a countermeasure for slope stability, as reported by Xue et al. (2015). In view of this record, this paper analyzed the seepage field, displacement field, stress field, and the corresponding stability of Badu landslide by using ABAQUS finite element software, considering rainfall and drainage conditions, respectively, thus aimed to evaluate the effect of drainage tunnel in Badu landslide. Four design schemes of drainage tunnel were used to compare their respective effect. The calculated results validated that rainfall contributed to the reactivation of Badu landslide, and also indicated drainage tunnel was an effective countermeasure to improve the landslide stability. Finally the most suitable scheme was proposed.