1. A real-time detection system for detecting the real-time machining by a rotating machine or rotating quality of a rotating machine comprising: a signal capture module for capturing a time-sequence signal of the rotating machine; a preprocessor coupled to the signal capture module for receiving the time-sequence signal and generating a stationary time-sequence signal by a Fourier Transform; a processor coupled to the preprocessor for receiving the stationary time-sequence signal and calculating a plurality of entropies of the stationary time-sequence signal by a predetermined way; and a comparison module with an entropy table or a feature judgment mechanism of the entropy variation, coupled to the processor, receiving the plurality of entropies and comparing the plurality of entropies according to the entropy table or the feature judgment mechanism of the entropy variation and generating a quality signal.