The invention discloses a method and apparatus for online detecting and cleaning up compact spinning yarn grid ring failure yarn faults. The method comprises the following steps of acquiring a yarn linear density signal, acquiring a voltage signal in direct proportion to the yarn linear density, acquiring a yarn VC% spectrogram via time domain analysis, acquiring a yarn signal power spectrum chart via frequency domain analysis and calculating a characteristic value of a characteristic function, and making a comparison between the characteristic value and a normal spectrum chart. When the comparison meets a grid ring yarn fault condition, the yarn of the section has grid ring yarn faults; and the yarn of the section is determined whether to be cut off according to the comparison between the VC% and the characteristic value. Yarn faults of the compact spinning yarn due to grid ring failure can be detected online; and the grid ring failure yarn faults can be cleaned up as needed.