The work aims to explore the influence of longitudinal-torsional ultrasonic grinding process parameters on the residual stress state of TC4 titanium alloy machining surface to improve the fatigue resistance of TC4 titanium alloy. The mechanical stress and thermal stress generated during the grinding process were analyzed based on the grinding force model of longitudinal-torsional ultrasonic grinding, the residual stress model of the longitudinal-torsional ultrasonic grinding surface was further established, and the residual stress distribution of the grinding process was obtained by MATLAB simulation. The finite element for a single abrasive particle under longitudinal-torsional ultrasonic grinding was established based on thermo- mechanical coupling, and the influence of grinding parameters on residual stress was analyzed, the rationality of the finite element model was verified by the longitudinal-torsional ultrasonic grinding experiment of TC4 titanium alloy. The residual stress of the TC4 titanium alloy ultrasonic grinding surface was the residual compressive stress, and the distribution curve of the stress along the depth of the workpiece was similar to the "tick". The residual compressive stress on the machined surface of the workpiece increased gradually with the increase of the grinding depth at first, when the grinding depth increased to 8 μm, the maximum value of the residual compressive stress was –488 MPa, and then decreased with the increase of the grinding depth. The residual compressive stress decreased with the increase of the grinding linear speed, and increased with the increase of the longitudinal-torsion ultrasonic amplitude. The average error between the simulation and experiment results of the residual stress on the machined surface was 9.8%, and changing trends of the residual stress were consistent. Longitudinal-torsion ultrasonic assisted grinding can effectively eliminate the residual tensile stress on the machined surface and obtain a more ideal residual compressive stress, which significantly improves the fatigue resistance of the TC4 titanium alloy.