The critical extrusion process of the fully dynamic recrystallization of the 690 alloy was analyzed by the Gleeble thermal compression experiment. The microstructure evolution model of 690 alloy was taken into the finite element (FE) software DEFORM-2D, and the secondary development of the FE software was carried based on the microstructure evolution during extrusion process. Then the influence of extrusion ratio, billet temperature and extrusion speed on the microstructure of 690 alloy were studied. The extrusion process control method for the microstructure o f 690 pipe according to the capacity of the extruder and the microstructure requirement. And further performing actual extrusion vertification based on the FE results. The results show that the grian size of the extrusion pipe decreases firstly and then increases with the increasing of extrusion ratio. The grain size of 690 extrusion pipe derceases with the decrease of billet temperature and extrusion speed. The grain size of the extruded pipe can bu controlled bellow 62.7μm when the billet temperature is 1200 ℃ and extrusion ratio is 15.3. The relative error between the simulation results and the extruded pipe is only 4.5%.