Laser assisted turning is an effective method machining difficult-to-machine materials such as ceramics, which uses a high power laser to focally heat a workpiece prior to material removal with a traditional cutting tool. A transient, three-dimensional heat transfer model was developed for laser assisted turning of silicon nitride using Finite Element Method to understand the thermal process of laser heating and to optimize the operating parameters. A laser assisted turning experiment system was set up to investigate the thermal conditions and cutting process of laser assisted turning of sintered silicon nitride and the experiments were conducted on the system using selected parameters. Effects of cutting parameters on cutting forces and specific cutting energy were investigated. Forces on the chip and SEM micrographs of chip morphology were studied to discuss the material removal mechanism of laser assisted turning of silicon nitride. Tool wear, surface roughness of the machined surface and the quality of subsurface were investigated. The results showed that the heat transfer model could be used to optimize the cutting parameters and laser assisted turning method could increase the machining efficiency while maintaining machining quality and reasonable levels of tool wear. A method of optimizing LAM based on the thermal model was presented.