Abstract: The hot extrusion process of Zr-2.5Nb alloy for CANDU pressure pipe was studied by using numerical simulation techniques. The results show that in hot extrusion of Zr-2.5Nb alloy, the conical die shall be used and the die angle shall be 90° to obtain a smaller peak extrusion pressure. When the heating temperature of the billet is 750-820℃, the local temperature of the alloy billet will exceed the β transition temperature due to friction and plastic deformation. At high heating and extrusion temperatures, the microstructure of the extruded tube blank changes from brick microstructure with long sheetα grain to Widmannstatten microstructure with needle α grain. The thermodynamic simulation result shows that the β phase transition temperature of the alloy mainly depends on the O content and is insensitive to the Nb content. The texture formation of the alloy will mainly depend on the Burgers relationship of the β→α at too fast extrusion speed, and the microstructure of the alloy will also deviate from the expected microstructure.