Abstract: Aiming at such problems as poor consistency of bolt preload in aero-engine assembly， the decline rule and distribution characteristics of bolt preload in sequential tightening and star tightening were studied based on the FEM of bolted rotors. The experimental study of bolt preload was carried out， the influence of tightening sequence and tightening speed on the bolt preload were analyzed， and then the decline mechanism of the preload over time was revealed. The results showed that the preload decreases significantly when the adjacent bolts are tightened，and increasing tightening speed will make the bolt get larger preload， which makes the connection structure more stable. After tightening the bolts， the preload will decline significantly in a short period of time， and the decline rule is closely related to the torque amplitude. Therefore， in engine assembly， the decline of preload in a short period of time cannot be ignored while strictly controlling the bolt tightening process.

Key words: bolted joint; tightening process; preload decline; residual preload; experimental research