A system for detecting an optical signal-to-noise ratio, OSNR, comprising a wavelength label loader and an OSNR detector, wherein the wavelength label loader is configured for loading a wavelength label signal of a frequency f1 to an optical signal by modulation encoding using an encoder, and sending a modulation depth corresponding to the wavelength label signal at the wavelength label loader to the OSNR detector; and the OSNR detector is configured for: analyzing the wavelength label signal to acquire a modulation depth corresponding to the wavelength label signal at the OSNR detector; and acquiring, according to the modulation depth corresponding to the wavelength label signal at the OSNR detector and the modulation depth corresponding to the wavelength label signal at the wavelength label loader, an OSNR of the optical signal, characterized in that the optical signal is of multiple wavelengths of an optical multiplexed section, wherein the encoder is an Electrically Variable Optical Attenuator and the modulation depth corresponding to the wavelength label signal at the wavelength label loader is sent to the OSNR detector via an Optical Supervision Channel, OSC, wherein the OSNR detector comprises a second optical splitter, a second optical tunable filter, a wavelength label information detecting unit, a second modulation depth detecting unit, and an OSNR acquiring unit, wherein the second optical splitter is configured for distributing the optical signal bearing the wavelength label signal, wherein the second optical tunable filter is configured for demultiplexing the optical signal distributed by the second optical splitter, wherein the wavelength label information detecting unit is configured for acquiring the modulation depth corresponding to the wavelength label signal at the wavelength label loader via the OSC, and sending the modulation depth corresponding to the wavelength label signal at the wavelength label loader to the OSNR acquiring unit, wherein the second modulation depth detecting unit is configured for analyzing the wavelength label signal to acquire the modulation depth corresponding to the wavelength label signal at the OSNR detector, and sending the modulation depth corresponding to the wavelength label signal at the OSNR detector to the OSNR acquiring unit, wherein the OSNR acquiring unit is configured for acquiring, according to the modulation depth corresponding to the wavelength label signal at the OSNR detector and the modulation depth corresponding to the wavelength label signal at the wavelength label loader, the OSNR of the optical signal; and adjusting the OSNR according to a frequency range of an Amplified Spontaneous Emission noise, wherein the wavelength label loader comprises a wavelength label loading unit, a first optical splitter, and a first modulation depth detecting unit, wherein the wavelength label loading unit is configured for loading the wavelength label signal to the optical signal, which is a high-speed optical signal; the first optical splitter is configured for distributing the optical signal bearing the wavelength label signal; and the first modulation depth detecting unit is configured for: analyzing the wavelength label signal loaded in the optical signal to acquire the modulation depth corresponding to the wavelength label signal at the wavelength label loader, wherein the wavelength label loader further comprises a first optical tunable filter configured for demultiplexing the optical signal distributed by the first optical splitter. the wavelength label loading unit is configured for loading the wavelength label signal to the optical signal, which is a high-speed optical signal; the first optical splitter is configured for distributing the optical signal bearing the wavelength label signal; and the first modulation depth detecting unit is configured for: analyzing the wavelength label signal loaded in the optical signal to acquire the modulation depth corresponding to the wavelength label signal at the wavelength label loader,