A finite element (FE) model for the extrusion process of large-scale thick-walled 304 stainless steel pipes was firstly developed based on DEFORM-2D platform, which can predict the DRX evolution behavior by coupling with a DRX model of 304 stainless steel. Secondly, the influence of the above key extrusion parameters on the average grain size and the grain uniformity of the extruded pipe were investigated by a liner orthogonal regression method. Finally, the influence laws of the key parameters on the average grain size and the grain uniformity were analyzed by a single factor method. The results show that extrusion speed V, initial billet temperature Tb and extrusion ratio λ have more obvious effects on the average grain size and the grain uniformity than other ones, and the influence sequences of these parameters to the average grain size and the grain uniformity are Tb>λ>V and Tb>V>λ, respectively. And the average grain size becomes smaller and the grain uniformity gets enhanced with the decrease of V and the increase of Tb and λ