Abstract: To address the issues of unclear torque and preload values for bolted connections in aircraft engines and their susceptibility to loosening during service, this study conducted multi-condition experimental research on three typical bolt/nut specifications: MJ5, MJ6, and MJ8. Torque-preload tests were performed under three different material conditions for connected components (graphite grease lubrication, 40CrNiMoA, ZL114A, and GH4169), analyzing the variation patterns of torque-preload coefficients. Through ultimate tightening failure tests, the load-bearing capacity of the connections was evaluated, and a safety factor of 0.7 was applied to determine the maximum installation preload. Loose tests were conducted under vibration conditions at 30 Hz and an amplitude of 11.43 mm to identify the minimum assembly torque required for anti-loosening. The results showed that graphite grease lubrication significantly reduces torque-preload coefficients and enhances preload, with parameter fluctuations of only 7% after repeated disassembly and assembly. Higher strength of connected components leads to better torque-to-preload conversion efficiency. Bolt failure under combined tension and torsion occurs prematurely, with its ultimate preload being 67.5%~81.9% of the measured tensile load. A tightening torque not less than 0.8 times the standard value can effectively prevent vibration-induced loosening. Based on the experimental data, recommended torque ranges for different nuts and connected component materials were derived, providing experimental support for the formulation of assembly processes and reliability improvement of bolted connections in aircraft engines.