<p>Monocrystalline silicon (mono-Si) is widely used in many fields due to its excellent properties. In recent years, with the continuous improvement of the quality requirements for mono-Si cutting, the ultrasonic-assisted diamond wire sawing (UADWS) has gradually developed. As a crucial factor affecting the machining quality, it is of great significance to accurately predict the sawing force. In this paper, based on the analysis of the critical cutting depth for brittle-to-ductile transition, abrasive trajectory, micro-mechanics of abrasives, and material removal volume, the force model for material removal by single abrasive in both brittle and ductile modes were established respectively. According to the distribution of abrasives on the surface of wire saw, the theoretical model of UADWS sawing force based on material brittle-ductile removal mode was constructed. The experiment of sawing mono-Si by UADWS was carried out, and the sawing force in the machining process was measured. The theoretical model was verified, and the influence of processing parameters on the sawing force was analyzed. The results show that the relative error between the theoretical and experimental results of normal force and tangential force is less than 12.13% and 16.67% respectively, which verifies the validity of the theoretical model. The sawing force increases with the increase of feed speed and decreases with the increase of wire speed and ultrasonic amplitude. The research results provide a reference for predicting sawing force and optimizing processing parameters in UADWS technology.</p>