As a third-generation semiconductor material, single crystal sapphire promises in LED substrates, laser components and visible windows, etc. Grinding is a critical intermediate finishing process to meet the demand for high productivity and good surface integrity in machining sapphire parts. However, as a typical hard-brittle (difficult-to-machine) material, its grinding process becomes increasingly difficult to predict let alone control. Moreover, subsurface damage during the grinding process is inevitably produced, which greatly increases the subsequent polishing time. In this research, a serial of grinding experiments was designed and carried out to explore the grinding mechanism and forecast product damage of single crystal sapphire. Grinding characteristics were investigated by monitoring grinding force and grinding power,  measuring surface roughness as well as testing subsurface damage. A monitor system by multi-sensor fusion was developed based on LabVIEW, integrating precision grinder, advanced sensors, data acquisition and analytical tools.  The section microscopy method was employed to detect the subsurface damage under an ultra-depth three-dimensional microscope. Meanwhile, the undeformed chip thickness and equivalent chip thickness were computed to reveal the effect of grinding parameters on the subsurface damage. The correlation between grinding power/energy and depth of cracks in the sapphire subsurface damage layer was analyzed. Research results show that there is a good mapping relationship between grinding energy and depth of the subsurface damage layer. The subsurface damage of single crystal sapphire could be predicted by monitoring the grinding signal and further optimized in proper grinding conditions.