A machine tool spindle structure capable of monitoring a working state in real time includes a spindle body, a rotating mandrel, a cutter base, and an internal inspecting device. The cutter base is combined with the rotating mandrel and rotates with the rotating mandrel. The rotating mandrel has a chamber, and the internal inspecting device is disposed in the chamber. Inspecting chips in the internal inspecting device are directly disposed on the cutter base, so as to measure working parameters during a processing process. The working parameters are transmitted to an external information device by a wireless transmission module in the internal inspecting device, thereby accurately giving a feedback of the working state of a processing cutter in real time.