The work aims to improve the resistance welding interface strength of titanium alloy-composite. A combination of stainless-steel mesh, prepreg and resin film was used as the interface implant, and the titanium alloy and the glass fiber reinforced polyetherimide (GF/PEI) laminate were connected by pulse resistance welding technology. The smooth surface of the titanium alloy was ground mechanically by abrasive sand and etched by H2O2/NaOH alkaline mixed solution. The chemical components, surface morphology and roughness of the titanium alloy were analyzed by energy dispersive spectrometer (EDS), scanning electron microscope (SEM) and static contact angle tester. Resistance welding was carried out to the titanium alloy with surface treated and the GF/PEI laminate, and the weldment was subjected to a single lap tensile shear test to evaluate the strength of the welded joint. The failure mode of the joint was verified by ultrasonic scanning microscopy to detect the internal damage of the laminate. After the titanium alloy was ground mechanically, the surface roughness increased and the contact angle increased from 56.8° to 84.8°. The interfacial bonding properties of titanium alloy and PEI resin increased, and the maximum welding strength was increased by 187.0%. The surface morphology of the titanium alloy after etched by alkaline mixed solution etching showed different structures with the increase of etching time (te), and a submicron network structure appeared in the later stage of etching. At the same time, the surface contact angle increased from 56.8° to 136.3°. The submicron network structure of the titanium alloy surface formed a mechanical interlocking structure with the PEI resin to jointly bear the mechanical properties of the welded joint, and the maximum welding strength was increased by 198.4%. The joint failure analysis showed that the main failure mode of the joint at the initial stage of welding was that the titanium alloy was directly peeled off from the interface. When the strength of the weldment achieved optimal, the failure mode was changed into the fracture of the implant. Mechanical grinding and etching of the titanium alloy can effectively improve the surface roughness, thereby improving the strength of welding joint of the titanium alloy-GF/PEI laminate.