The invention discloses a pre-tightening type assembly method suitable for an ultra-large compressor main shaft. The pre-tightening type assembly method comprises the following steps: analyzing a holediameter of a connecting hole of a to-be-assembled main shaft section, and selecting a screw of a lining which can be in interference fit to the connecting hole as a connecting screw, wherein the lining is arranged on the middle position in a sleeving mode; axially moving the connecting screw in the connecting hole, and enabling the lining to be in interference fit to a joint of two main shaft sections in the connecting hole; and separately tightening nuts at the two ends of the connecting screw, tightening a nut at one stretched side of the screw after a stretching machine stretches the connecting screw, releasing oil pressure of the stretching machine, fixing the connecting screw in two main shaft sections, thereby accomplishing connection of the two main shaft sections. According to the pre-tightening type assembly method disclosed by the invention, the side surface of the lining is in zero interference fit to the main shaft connecting hole, so that the two connected main shaft sections are free of radial relative displacement, and therefore, natural bow of the ultra-large compressor main shaft is eliminated, and continuous operation reliability of the ultra-large compressor main shaft is improved.