Abstract: In the northern structure of Bozhong 19-6 surrounding area, the Bohai Basin, the burial depth of the reservoir is over 4 500 m, the average drilling depth is more than 5 500 m, and the target horizon, i.e., the Archean basement is lithologically composed of granite gneiss, whose maximum compression strength is over 200 MPa, abrasivity is strong and rate of penetration (ROP) is only 1-4 m/h, which seriously restricts the efficient development of this block. In order to improve the drilling efficiency in the target block, this paper established the work expression of weight on bit (WOB), torque, rock breaking and friction, respectively from the perspective of energy conservation in the process of drilling, based on the mechanical specific energy theory. Then, the energy input-output balance equation of rock breaking process was created. The practical application results show that the energy balance equation can provide a reasonable WOB range by using the basic parameters of the formation to be drilled. The recommended optimal WOB is in line with the actual drilling data and the average error of the predicted ROP is 8%, indicating good applicability. The research results provide a design basis for the optimization of subsequent deep and ultra-deep well drilling operation.