The invention provides a preparation method of a titanium implant surface with a micro-nano composite structure. The preparation method comprises the following steps: (1) performing blast sanding and ultrasonic processing on a smooth implant surface, then washing with water, and drying; (2) processing the implant surface in an oxalic acid solution for 30-240 min, then washing with water, and drying, wherein the concentration of the oxalic acid solution is 30% to saturation; and (3) taking a mixed acid solution of H2SO4 with the concentration of 98% and H2O2 with the concentration of 30% for processing, and then washing with water to obtain the titanium implant surface with the micro-nano composite structure. According to the preparation method of the titanium implant surface with the micro-nano composite structure, disclosed by the invention, the implant surface with the micro-nano composite structure is obtained by performing a secondary etching on a micron-structure surface processed by sand blast and oxalic acid, and compared to the micron-structure surface, titanium implant surface is provided with a microstructure with more levels, which is capable of providing more comprehensive environment signals for cell growth and tissue regeneration; and the titanium implant surface with the micro-nano composite structure has super-hydrophilicity and the protein adsorption capability is remarkably enhanced, which are of a great significance to further improving the surface biological activity of implants.