<p>Longitudinal Torsional Ultrasonic Grinding (LTUG) is an effective machining technique for reducing the grinding force of Ti-6Al-4V and improving surface integrity. However, existing mechanical modeling studies on LTUG of Ti-6Al-4V typically predict only the average grinding force and do not account for the stochastic distribution of abrasive grains or the contact–separation behavior induced by ultrasonic vibration. Under the background, the LTUG force model for Ti-6Al-4V was established by considering the random distribution of grains. Firstly, the net cutting time model of LTUG was established and applied to analyze the dynamic contact–separation characteristics between abrasive grains and the workpiece. Then, the wheel surface morphology model was built based on the random distribution of positions and geometries grain, and the criteria for distinguishing cutting stages during LTUG were investigated. Subsequently, the single-grain grinding force model under LTUG of titanium alloys was developed. By considering these factors, the LTUG force model was established. The results demonstrate that the proposed LTUG force model achieves high prediction accuracy, with errors ranging from 2.7–16.1% relative to experimental results. Notably, localized high grinding force generated by specific grains are the main contributors to elevated grinding temperatures and degraded machining quality, which can be effectively mitigated by LTUG through reducing the overall grinding force of abrasive grains. Compared with conventional grinding, grinding force are reduced by up to 51.1% under LTUG. It provides theoretical support for grinding force prediction and process parameter design in precision grinding of Ti-6Al-4V components.</p> Graphical abstract <p></p>