<p>Hard and brittle materials such as sapphire are prone to surface defects, severe tool wear and low machining efficiency during machining. Although fly-cutting produces high-quality surfaces, it is still challenged by short tool life and surface failures when machining hard and brittle materials. Laser-assisted machining has attracted attention for its ability to improve material surface quality and tool life, but the feasibility of combining it with fly-cutting has not yet been clarified. In this paper, a method of laser-assisted heat treatment (LAHT) combined with fly-cutting machining is proposed, and its machining mechanism is discussed in depth through theoretical modelling and experimental research. The analytical relational equations between the position of the maximum undeformed cutting thickness and the rotational radius, feed, and rotation angle were resolved by modelling the maximum undeformed cutting thickness and cutting force. A systematic analysis was conducted to investigate the influence of laser power, rotational speed and tool direction on the material deformation mechanism. Comparative experiments showed that LAHT significantly reduced cutting forces and power spectral density at the intrinsic frequency of the dynamometer, reduced tool wear and improved machining efficiency. At the same time, laser-assisted heat-treating fly-cutting drastically improves groove quality, with reduced cracking, improved integrity, and a tendency to achieve higher material removal efficiencies and plasticity removal by appropriately increasing the rotational speed in the low-speed region. Finite element simulations show that laser heat treatment effectively reduces machining stresses and residual stresses. It was also found that diamond tool face forward machining resulted in a smoother and flatter surface quality. The feasibility and advantages of laser-assisted heat-treated fly-cutting machining in the image-based processing of hard and brittle material surfaces are verified by successfully preparing high-quality microgrid patterns on the sapphire surface through the method of crossing and overlapping. The study shows that this method significantly improves the processing quality and efficiency, and provides a new idea for high-precision processing of hard and brittle materials.</p> Graphical Abstract <p></p>