In this work, the numerical and experimental investigation on extrusion process of a three-cavity aluminum profile has been carried out. Firstly, the extrusion process of the profile was simulated using FE (finite element) code Hyper Xtrude. The velocity distribution and the material flow behavior during the extrusion process have been investigated. Taking into consideration of the severe non-uniformity of the velocity distribution, a series of adjustments of the initial die structure have been taken, such as the modification of drainage channels, the introduction of baffle plates, and the variation of local bearing lengths. Experimentally, a real extrusion die was manufactured and the aluminum profile has been extrudated on an 80 MN extrusion press. By comparing with the nose-end of the extrudate obtained by experiments, the numerical results and die modification methods were well validated, which can provide theoretical guidelines for the die design of this kind of profile.