The study on improving the erosion wear resistance of TC21 titanium alloy through laser peening (LP) was carried out. The residual stress and full width half maximum (FWHM) in the gradient direction of the specimens before and after LP was analyzed, while the in-depth microhardness was also tested. The microstructural response generated by LP was observed using electron backscattered diffraction (EBSD). The erosion wear properties of differently processed specimens were finally trialed. The results indicated that LP effectively enhanced the erosion wear resistance of TC21 titanium alloy by generating grain refinement and compressive residual stress (CRS) without much deterioration of the surface roughness.