Abstract: Aiming at the ambiguous determination of tightening torque and preload, as well as the prevalent loosening risk of bolted joints in aero engines, three typical fastener sizes (MJ5, MJ6 and MJ8) were selected as research objects. Torque preload tests were carried out under two surface conditions, i.e., graphite grease lubrication and dry without lubrication, for bolt nut pairs made of 40CrNiMoA, ZL114A and GH4169. The evolution characteristics of torque tension coefficient and preload were analyzed. Ultimate tightening failure tests were performed to evaluate the ultimate load bearing capacity and determine the maximum allowable assembly preload of the bolted connections. Furthermore, loosening tests were implemented under practical service conditions with a vibration frequency of 30 Hz and displacement amplitude of 11.43 mm, so as to identify the minimum assembly torque required for anti loosening performance. The experimental results demonstrate that graphite grease lubrication effectively reduces the torque tension coefficient and improves the achievable preload. Higher strength of the clamped component contributes to superior conversion efficiency from tightening torque to preload. The findings of this work can provide experimental support for assembly process formulation and reliability improvement of aero engine bolted joints.