The work aims to obtain optimal process parameters, and study effects of process parameters and their interactions on surface quality of workpieces. 2D ultrasonic extrusion processing test was performed to 7075 aluminum alloy in the method of orthogonal test. Influence weight of surface roughness and microhardness was determined in entropy weight method. Optimal evaluation model of surface quality was built by combining grey correlation method and TOPSIS method. Optimal process parameters for the best surface quality were obtained. The effects of process parameters and their interactions on the surface quality were studied based upon range analysis. The surface roughness values decreased substantially and the surface microhardness increased significantly after 2D ultrasonic extrusion processing. The optimal process parameters could be obtained accurately by the as-built evaluation model. Provided with static force of 300 N, extrusion speed of 30 m/min and feed-rate of 0.1 mm/r, the optimal surface quality may be obtained with surface roughness Ra of 0.41 μm and microhardness of nearly 378HV. The effect of interactions among processing parameters on surface roughness, microhardness and surface quality is far greater than the main effect. The interaction between static force and extrusion speed as well as the interaction between extrusion speed and feed-rate play a major role on surface overall quality.