The invention relates to a method and device for detecting noise of an erbium-doped optical fiber amplifier in real time. The amplifying gain G of the optical fiber amplifier and the ase power Pase generated by the optical fiber amplifier are obtained through calculation by detecting in-band signal luminous power, out-of-band short-wavelength luminous power and out-of-band long-wavelength luminous power of detected light signals at the input end of the optical fiber amplifier and detecting in-band signal luminous power, out-of-band short-wavelength luminous power and out-of-band long-wavelength luminous power of detected light signals at the output end of the optical fiber amplifier, and the noise level NF of the detected optical fiber amplifier is obtained through estimation. Therefore, real-time evaluation of the noise of the optical fiber amplifier can be carried out on the premise of not affecting light signal transmission quality, whether the optical fiber amplifier normally works is judged, and certain basis is provided for fault diagnosis of an optical fiber communication line.