Melt-spun surface structured fiber could be a large-scale versatile platform for materials with advanced surface function and local properties. Fibers with distinct surface and bulk structures are developed by tailoring the viscosity ratio and blend ratio of polymer component using the melt-spinning method. Spherical bulge and fibril groove structured fibers are obtained in different viscosity ratio and blend ratio systems. The interfacial bonding between fiber and matrix is improved due to the mechanical interlocking between the structured surface and matrix. The low-viscosity second phase stays as a spherical droplet even in high content. The second phase in matched- and high-viscosity ratio cases is deformed into fibril like droplet which causes an in-situ fibration of the second phase in polymer blend fiber with an enhanced mechanical property. This method provides a simple route to developing polymer materials with surface structure and appropriate mechanical properties to apply in textile and polymer fiber-reinforced composite materials.