A grinding method is provided in which abrasive is projected onto a steel product through a nozzle to perform grinding thereon such as in a continuous casting process or in a subsequent process, wherein high-pressure water jet mixed with the abrasive is projected onto the surface of the steel product to grind defects on the surface, etc. thereof. A grinding system for executing this grinding method is also provided, the system including supply sources of high-pressure liquid and abrasive, a nozzle device connected with these supply sources, an abrasive recovery device for recovering the used abrasive as needed and restoring the same to the supply sources, and combined detection systems.