In this paper, surface morphologies of Ti-6Al-4V forging and powder metallurgy workpieces were characterized, surface roughness mathematical models of the two machined workpieces were developed using orthogonal regression test,and the significances of the mathematical models were verified, the surface roughness mathematical models could predict the surface roughness changing trends. The experimental results showed that feed scratch, chip fragment and surface tearing defects appeared in the machined Ti-6Al-4V forging surface, while micro-void defect was formed in the machined powder metallurgy material surface apart from the feed scratch, chip fragment and surface tearing defects.The influence of feed rate on the surface roughness of both workpieces is greatest, and the existence of internal micro-void of Ti-6Al-4V powder metallurgy material led influence of cutting speed greater.