The fixed dummy block bears high temperature, high pressure, and friction under complex working condition. The three dimensional finite element analysis model of fixed dummy block of 55 MN aluminum extrusion press was established using finite element software MSC.Marc, which includes pad block, outer jacket, and fastening pad block as deformation contact body, and considering temperature effect, the thermal-structure analysis was carried out using direct coupling method. It indicates that working surface node radial expansion of the outer jacket is gradually incremental with successive working load, and has three different increase intervals of rapid, slow and steady rate. These conclusions provide a reference for optimal design of fixed dummy block.