The friction design principle of highstrength bolt connection pair was described, and the M42 bolt of a large wind turbine was taken as the research object. The finite element method was used to apply different friction coefficient to the bolt connection pair, the stress of the bolt under different friction coefficient was calculated, and the friction coefficient of the joint pair at this part was tested by experiment. The results show that the friction coefficient of the joint pair has a great influence on the bolt stress, but there is a big deviation between the measured friction coefficient and the conventional design friction coefficient. If the friction coefficient is designed according to the conventional design, the system will become very large and the cost will increase greatly. These studies provide reference for of bolted connections refinement design and cost reduction of system.