Preloading　the　high　strength　bolt　using　hydraulic　extension　method　is　a　fast　and　efficient　method　for　bolt　installation.　Hydraulic　bolt　tension　device　can　guarantee　the　initial　tension　of　bolt　well.　However,　if　the　relation　of　initial　tension　and　the　final　remaining　preload　of　bolt　cannot　be　determined,　the　preload　on　the　bolts　still　cannot　be　guaranteed.　This　paper　uses　theoretical　analysis　method　to　research　the　relation　between　the　eventual　preload　and　the　initial　tension　of　high　strength　bolts　on　Heavy-duty　Gantry　beams.　Then　we　propose　a　set　of　calculation　method　of　bolt　installation　preload　and　the　initial　tension　and　provide　theoretical　basis　for　the　installation　of　heavy-duty　segmented　beam.