Abstract: The supersonic fine particle bombardment (SFPB) surface nanocrystallization technique is used to construct a gradient nanostructure with a certain layer depth on the surface of TC11 alloy, and the effect of SFPB gas pressure on the microstructure and mechanical properties of TC11 alloy is investigated. The results showed that a 25 μm-thick of severe plastic deformed layer is formed at a small gas pressure (0.5 MPa), and the surface grains are refined to the nanometer scale (17.7 nm). With the increase of gas pressure, the surface nanocrystal size decreases and the SPD layer increases. At the high gas pressure (1.5 MPa), the surface nanocrystal size and the depth of SPD layer are 9.4 nm and 51 μm, respectively. With the increase of SFPB gas pressure, the surface microhardness and the depth of hardened layer gradually increase, and the yield and tensile strengths increase significantly, while the elongation does not change much. The fracture morphology changes from the typical ductile fracture to the mixed ductile-brittle fracture.