During hot extrusion process, die wear shortens markedly the service life of extrusion dies under the high-pressure, high-temperature conditions. In this paper, based on modified Archard's wear model, a user-defined subroutine for calculating die wear depth was developed and implanted into DEFORM-3D. On the basis of the numerical model, the die wear behavior during aluminum alloy 7075 tube extrusion has been investigated. The numerical results show that process variables have multiple effects on die wear behavior. With the increasing ram speed, wear depth of die bearing rises and then tends to decline gradually. From the ram speed of 15 mm/s, die wear depth begins to increase again. Wear depth rises suddenly with the increase of friction coefficient, then gradually reduces. When friction coefficient is greater than 0.8, wear depth tends to be a constant. A maximum wear depth occurs at 430 °C of billet temperature, and a minimum wear depth occurs at certain die temperature in the range of 400–425 °C. In addition, the required extrusion force has strong dependence on process variables. The extrusion force rises clearly with the increase of ram speed and friction coefficient and with the decrease of initial temperatures of billet and die.