Unlike conventional sidetracking technology, the technology of reaming while directional drilling makes it possible for us to conduct directional drilling and reaming simultaneously using dual core bit, which simplifies the construction steps and can greatly shorten the drilling cycle and reduce drilling costs. With the increasing of the tasks of sidetrack horizontal well in the old wells of Tahe Oilfield, the technology of reaming while directional drilling has become an important means for sidetrack of old wells in Tahe Oilfield. However the substratum of Bachu formation has high content of gravel with large diameter and strong consolidation, which cause severe abrasion of dual core bit, short drill life and low ROP. With the problems in the substratum of Bachu Formation, Tahe Oilfield continuously improves dual core bit based on its effect of reaming while drilling, and breaks the national records of the maxim setting depth, inclination and continuous expansion length during the operations of well TH12124CH. This paper shows the improvements of dual core bit and its application effect both in well TH10233CH and well TH12124CH, and put forward a further scheme to improve the dual core bit for the substratum of Bachu Formation of Tahe Oilfield.