<p>Machining with active soft abrasives that react with sapphire in the solid phase is a highly efficient and low-damage machining method with great potential. It provides an effective technical approach for solving the problem of hard and brittle material machining. This study constructed a theoretical model of the reaction-layer thickness (RLT) based on the contact state between the SiO₂ abrasives and sapphire, and scratch tests were used to verify the model. Based on the model, the influence trends of the rotational speed, loading pressure, abrasive size, and abrasive content on the reaction layer thickness and material removal rate (MRR) were analyzed. In addition, the influence of changes in process parameters on the evolution of the reaction layer is discussed. The results show that the experimentally measured reaction layer thickness is from 4.42 nm to 21.97 nm, and the average thickness estimated by the model is from 5.6 nm to 19.1 nm, which verifies the reliability and accuracy of the model. With an increase in the rotation speed, the friction effect was enhanced and the temperature of the contact area increased. However, the reaction time of the microcontact area decreased, resulting in a decrease in the reaction layer thickness. Increasing the loading pressure and abrasive content and reducing the abrasive size can increase the number of effective abrasive grains and the contact area, enhance the reactivity and reaction rate with sapphire, and promote the formation of the reaction layer. These findings provide a theoretical basis for optimizing the lapping process and a new perspective for understanding the evolution of the reaction layer and material removal mechanism.</p>